diff --git a/eng/targets/CSharp.Common.targets b/eng/targets/CSharp.Common.targets
index 2d9deb5890..c9ef556f4d 100644
--- a/eng/targets/CSharp.Common.targets
+++ b/eng/targets/CSharp.Common.targets
@@ -13,6 +13,9 @@
 
     <!-- Public members should not use oblivious types. Not done with all nullable annotations. -->
     <NoWarn>$(NoWarn);RS0041</NoWarn>
+
+    <!-- Turn off platform compatiblity analyzer warnings in test, test assets, and samples -->
+    <NoWarn Condition="'$(IsTestProject)' == 'true' OR '$(IsTestAssetProject)' == 'true' OR '$(ISBenchmarkProject)' == 'true' OR '$(IsSampleProject)' == 'true'">$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
 
   <ItemGroup Condition=" Exists('$(MSBuildProjectDirectory)\PublicAPI.*.txt') AND
diff --git a/global.json b/global.json
index a1861e99f3..ca240fa07a 100644
--- a/global.json
+++ b/global.json
@@ -1,9 +1,9 @@
 {
   "sdk": {
-    "version": "5.0.100-rc.1.20379.10"
+    "version": "5.0.100-rc.1.20429.2"
   },
   "tools": {
-    "dotnet": "5.0.100-rc.1.20379.10",
+    "dotnet": "5.0.100-rc.1.20429.2",
     "runtimes": {
       "dotnet/x64": [
         "2.1.18",
diff --git a/src/Components/Ignitor/src/CancellableOperation.cs b/src/Components/Ignitor/src/CancellableOperation.cs
index 6e1f217d19..4498440800 100644
--- a/src/Components/Ignitor/src/CancellableOperation.cs
+++ b/src/Components/Ignitor/src/CancellableOperation.cs
@@ -14,7 +14,7 @@ namespace Ignitor
         {
             Timeout = timeout;
 
-            Completion = new TaskCompletionSource<TResult>(TaskContinuationOptions.RunContinuationsAsynchronously);
+            Completion = new TaskCompletionSource<TResult>(TaskCreationOptions.RunContinuationsAsynchronously);
             Completion.Task.ContinueWith(
                 (task, state) =>
                 {
diff --git a/src/Components/test/E2ETest/ServerExecutionTests/CircuitGracefulTerminationTests.cs b/src/Components/test/E2ETest/ServerExecutionTests/CircuitGracefulTerminationTests.cs
index 69c20cb970..eb3340427e 100644
--- a/src/Components/test/E2ETest/ServerExecutionTests/CircuitGracefulTerminationTests.cs
+++ b/src/Components/test/E2ETest/ServerExecutionTests/CircuitGracefulTerminationTests.cs
@@ -47,7 +47,7 @@ namespace Microsoft.AspNetCore.Components.E2ETest.ServerExecutionTests
             Browser.MountTestComponent<CounterComponent>();
             Browser.Equal("Current count: 0", () => Browser.FindElement(By.TagName("p")).Text);
 
-            GracefulDisconnectCompletionSource = new TaskCompletionSource<object>(TaskContinuationOptions.RunContinuationsAsynchronously);
+            GracefulDisconnectCompletionSource = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
             Sink = _serverFixture.Host.Services.GetRequiredService<TestSink>();
             Messages = new List<(Extensions.Logging.LogLevel level, string eventIdName)>();
             Sink.MessageLogged += Log;
diff --git a/src/DataProtection/DataProtection/src/DataProtectionBuilderExtensions.cs b/src/DataProtection/DataProtection/src/DataProtectionBuilderExtensions.cs
index 7789ca074f..e6618bd535 100644
--- a/src/DataProtection/DataProtection/src/DataProtectionBuilderExtensions.cs
+++ b/src/DataProtection/DataProtection/src/DataProtectionBuilderExtensions.cs
@@ -4,6 +4,7 @@
 using System;
 using System.ComponentModel;
 using System.IO;
+using System.Runtime.Versioning;
 using System.Security.Cryptography.X509Certificates;
 using Microsoft.AspNetCore.Cryptography;
 using Microsoft.AspNetCore.DataProtection.AuthenticatedEncryption;
@@ -223,6 +224,7 @@ namespace Microsoft.AspNetCore.DataProtection
         /// <param name="builder">The <see cref="IDataProtectionBuilder"/>.</param>
         /// <param name="registryKey">The location in the registry where keys should be stored.</param>
         /// <returns>A reference to the <see cref="IDataProtectionBuilder" /> after this operation has completed.</returns>
+        [SupportedOSPlatform("windows")]
         public static IDataProtectionBuilder PersistKeysToRegistry(this IDataProtectionBuilder builder, RegistryKey registryKey)
         {
             if (builder == null)
@@ -356,6 +358,7 @@ namespace Microsoft.AspNetCore.DataProtection
         /// <remarks>
         /// This API is only supported on Windows platforms.
         /// </remarks>
+        [SupportedOSPlatform("windows")]
         public static IDataProtectionBuilder ProtectKeysWithDpapi(this IDataProtectionBuilder builder)
         {
             if (builder == null)
@@ -378,6 +381,7 @@ namespace Microsoft.AspNetCore.DataProtection
         /// <remarks>
         /// This API is only supported on Windows platforms.
         /// </remarks>
+        [SupportedOSPlatform("windows")]
         public static IDataProtectionBuilder ProtectKeysWithDpapi(this IDataProtectionBuilder builder, bool protectToLocalMachine)
         {
             if (builder == null)
@@ -408,6 +412,7 @@ namespace Microsoft.AspNetCore.DataProtection
         /// See https://msdn.microsoft.com/en-us/library/windows/desktop/hh706794(v=vs.85).aspx
         /// for more information on DPAPI-NG. This API is only supported on Windows 8 / Windows Server 2012 and higher.
         /// </remarks>
+        [SupportedOSPlatform("windows")]
         public static IDataProtectionBuilder ProtectKeysWithDpapiNG(this IDataProtectionBuilder builder)
         {
             if (builder == null)
@@ -435,6 +440,7 @@ namespace Microsoft.AspNetCore.DataProtection
         /// and <paramref name="flags"/> arguments.
         /// This API is only supported on Windows 8 / Windows Server 2012 and higher.
         /// </remarks>
+        [SupportedOSPlatform("windows")]
         public static IDataProtectionBuilder ProtectKeysWithDpapiNG(this IDataProtectionBuilder builder, string protectionDescriptorRule, DpapiNGProtectionDescriptorFlags flags)
         {
             if (builder == null)
diff --git a/src/DataProtection/DataProtection/src/KeyManagement/XmlKeyManager.cs b/src/DataProtection/DataProtection/src/KeyManagement/XmlKeyManager.cs
index 736005ecf7..094832e43c 100644
--- a/src/DataProtection/DataProtection/src/KeyManagement/XmlKeyManager.cs
+++ b/src/DataProtection/DataProtection/src/KeyManagement/XmlKeyManager.cs
@@ -7,6 +7,7 @@ using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
 using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 using System.Threading;
 using System.Xml;
 using System.Xml.Linq;
@@ -500,6 +501,8 @@ namespace Microsoft.AspNetCore.DataProtection.KeyManagement
                 {
                     if (OSVersionUtil.IsWindows())
                     {
+                        Debug.Assert(RuntimeInformation.IsOSPlatform(OSPlatform.Windows)); // Hint for the platform compatibility analyzer.
+
                         // If the user profile is available, we can protect using DPAPI.
                         // Probe to see if protecting to local user is available, and use it as the default if so.
                         encryptor = new DpapiXmlEncryptor(
@@ -523,10 +526,14 @@ namespace Microsoft.AspNetCore.DataProtection.KeyManagement
                     RegistryKey regKeyStorageKey = null;
                     if (OSVersionUtil.IsWindows())
                     {
+                        Debug.Assert(RuntimeInformation.IsOSPlatform(OSPlatform.Windows)); // Hint for the platform compatibility analyzer.
                         regKeyStorageKey = RegistryXmlRepository.DefaultRegistryKey;
                     }
                     if (regKeyStorageKey != null)
                     {
+                        Debug.Assert(RuntimeInformation.IsOSPlatform(OSPlatform.Windows)); // Hint for the platform compatibility analyzer.
+                        regKeyStorageKey = RegistryXmlRepository.DefaultRegistryKey;
+
                         // If the user profile isn't available, we can protect using DPAPI (to machine).
                         encryptor = new DpapiXmlEncryptor(protectToLocalMachine: true, loggerFactory: _loggerFactory);
                         repository = new RegistryXmlRepository(regKeyStorageKey, _loggerFactory);
diff --git a/src/DataProtection/DataProtection/src/Microsoft.AspNetCore.DataProtection.csproj b/src/DataProtection/DataProtection/src/Microsoft.AspNetCore.DataProtection.csproj
index 8f16e33480..520a9f4745 100644
--- a/src/DataProtection/DataProtection/src/Microsoft.AspNetCore.DataProtection.csproj
+++ b/src/DataProtection/DataProtection/src/Microsoft.AspNetCore.DataProtection.csproj
@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <Description>ASP.NET Core logic to protect and unprotect data, similar to DPAPI.</Description>
@@ -14,6 +14,8 @@
 
   <ItemGroup>
     <Compile Include="..\..\shared\src\*.cs" />
+    <Compile Include="$(SharedSourceRoot)PlatformAttributes.cs"
+             Condition="'$(TargetFramework)' != '$(DefaultNetCoreTargetFramework)'" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/DataProtection/DataProtection/src/RegistryPolicyResolver.cs b/src/DataProtection/DataProtection/src/RegistryPolicyResolver.cs
index d3357fa34d..b1ec26ff12 100644
--- a/src/DataProtection/DataProtection/src/RegistryPolicyResolver.cs
+++ b/src/DataProtection/DataProtection/src/RegistryPolicyResolver.cs
@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.Versioning;
 using Microsoft.AspNetCore.Cryptography;
 using Microsoft.AspNetCore.DataProtection.AuthenticatedEncryption.ConfigurationModel;
 using Microsoft.AspNetCore.DataProtection.Internal;
@@ -17,6 +18,7 @@ namespace Microsoft.AspNetCore.DataProtection
     /// <summary>
     /// A type which allows reading policy from the system registry.
     /// </summary>
+    [SupportedOSPlatform("windows")]
     internal sealed class RegistryPolicyResolver: IRegistryPolicyResolver
     {
         private readonly Func<RegistryKey> _getPolicyRegKey;
diff --git a/src/DataProtection/DataProtection/src/Repositories/RegistryXmlRepository.cs b/src/DataProtection/DataProtection/src/Repositories/RegistryXmlRepository.cs
index 7692d1ccb5..28a7cbec23 100644
--- a/src/DataProtection/DataProtection/src/Repositories/RegistryXmlRepository.cs
+++ b/src/DataProtection/DataProtection/src/Repositories/RegistryXmlRepository.cs
@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using System.Runtime.Versioning;
 using System.Security.Principal;
 using System.Xml.Linq;
 using Microsoft.Extensions.Logging;
@@ -15,6 +16,7 @@ namespace Microsoft.AspNetCore.DataProtection.Repositories
     /// <summary>
     /// An XML repository backed by the Windows registry.
     /// </summary>
+    [SupportedOSPlatform("windows")]
     public class RegistryXmlRepository : IXmlRepository
     {
         private static readonly Lazy<RegistryKey> _defaultRegistryKeyLazy = new Lazy<RegistryKey>(GetDefaultHklmStorageKey);
diff --git a/src/DataProtection/DataProtection/src/XmlEncryption/DpapiNGXmlEncryptor.cs b/src/DataProtection/DataProtection/src/XmlEncryption/DpapiNGXmlEncryptor.cs
index f5162496bb..edd3afd493 100644
--- a/src/DataProtection/DataProtection/src/XmlEncryption/DpapiNGXmlEncryptor.cs
+++ b/src/DataProtection/DataProtection/src/XmlEncryption/DpapiNGXmlEncryptor.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Globalization;
+using System.Runtime.Versioning;
 using System.Security.Principal;
 using System.Xml.Linq;
 using Microsoft.AspNetCore.Cryptography;
@@ -18,6 +19,7 @@ namespace Microsoft.AspNetCore.DataProtection.XmlEncryption
     /// <remarks>
     /// This API is only supported on Windows 8 / Windows Server 2012 and higher.
     /// </remarks>
+    [SupportedOSPlatform("windows")]
     public sealed class DpapiNGXmlEncryptor : IXmlEncryptor
     {
         private readonly ILogger _logger;
diff --git a/src/DataProtection/DataProtection/src/XmlEncryption/DpapiXmlEncryptor.cs b/src/DataProtection/DataProtection/src/XmlEncryption/DpapiXmlEncryptor.cs
index d7fa2d7b1b..cd842f1acd 100644
--- a/src/DataProtection/DataProtection/src/XmlEncryption/DpapiXmlEncryptor.cs
+++ b/src/DataProtection/DataProtection/src/XmlEncryption/DpapiXmlEncryptor.cs
@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Runtime.Versioning;
 using System.Security.Principal;
 using System.Xml.Linq;
 using Microsoft.AspNetCore.Cryptography;
@@ -16,6 +17,7 @@ namespace Microsoft.AspNetCore.DataProtection.XmlEncryption
     /// <remarks>
     /// This API is only supported on Windows platforms.
     /// </remarks>
+    [SupportedOSPlatform("windows")]
     public sealed class DpapiXmlEncryptor : IXmlEncryptor
     {
         private readonly ILogger _logger;
diff --git a/src/Hosting/WindowsServices/src/Properties/AssemblyInfo.cs b/src/Hosting/WindowsServices/src/Properties/AssemblyInfo.cs
index 63d95d6dfb..6e6ee3ba7f 100644
--- a/src/Hosting/WindowsServices/src/Properties/AssemblyInfo.cs
+++ b/src/Hosting/WindowsServices/src/Properties/AssemblyInfo.cs
@@ -2,5 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Runtime.CompilerServices;
+using System.Runtime.Versioning;
 
 [assembly: InternalsVisibleTo("Microsoft.AspNetCore.Hosting.WindowsServices.Tests, PublicKey=0024000004800000940000000602000000240000525341310004000001000100f33a29044fa9d740c9b3213a93e57c84b472c84e0b8a0e1ae48e67a9f8f6de9d5f7f3d52ac23e48ac51801f1dc950abe901da34d2a9e3baadb141a17c77ef3c565dd5ee5054b91cf63bb3c6ab83f72ab3aafe93d0fc3c2348b764fafb0b1c0733de51459aeab46580384bf9d74c4e28164b7cde247f891ba07891c9d872ad2bb")]
+[assembly: SupportedOSPlatform("windows")]
\ No newline at end of file
diff --git a/src/Http/Http.Extensions/test/HeaderDictionaryTypeExtensionsTest.cs b/src/Http/Http.Extensions/test/HeaderDictionaryTypeExtensionsTest.cs
index 06c0d967e6..2ca3c36e27 100644
--- a/src/Http/Http.Extensions/test/HeaderDictionaryTypeExtensionsTest.cs
+++ b/src/Http/Http.Extensions/test/HeaderDictionaryTypeExtensionsTest.cs
@@ -162,7 +162,7 @@ namespace Microsoft.AspNetCore.Http.Headers
         {
             public static bool TryParse(string value, out TestHeaderValue result)
             {
-                if (string.Equals("valid", value))
+                if (string.Equals("valid", value, StringComparison.Ordinal))
                 {
                     result = new TestHeaderValue();
                     return true;
@@ -176,7 +176,7 @@ namespace Microsoft.AspNetCore.Http.Headers
                 var results = new List<TestHeaderValue>();
                 foreach (var value in values)
                 {
-                    if (string.Equals("valid", value))
+                    if (string.Equals("valid", value, StringComparison.Ordinal))
                     {
                         results.Add(new TestHeaderValue());
                     }
diff --git a/src/Http/Routing/test/UnitTests/Template/TemplateParserTests.cs b/src/Http/Routing/test/UnitTests/Template/TemplateParserTests.cs
index f5f36332e6..2ac022c212 100644
--- a/src/Http/Routing/test/UnitTests/Template/TemplateParserTests.cs
+++ b/src/Http/Routing/test/UnitTests/Template/TemplateParserTests.cs
@@ -896,7 +896,7 @@ namespace Microsoft.AspNetCore.Routing.Template.Tests
                 foreach (var xconstraint in x.InlineConstraints)
                 {
                     if (!y.InlineConstraints.Any<InlineConstraint>(
-                        c => string.Equals(c.Constraint, xconstraint.Constraint)))
+                        c => string.Equals(c.Constraint, xconstraint.Constraint, StringComparison.Ordinal)))
                     {
                         return false;
                     }
diff --git a/src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/BuildIntrospectionTest.cs b/src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/BuildIntrospectionTest.cs
index de73ff376a..c857f59ee4 100644
--- a/src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/BuildIntrospectionTest.cs
+++ b/src/Razor/Microsoft.NET.Sdk.Razor/integrationtests/BuildIntrospectionTest.cs
@@ -257,7 +257,7 @@ namespace Microsoft.AspNetCore.Razor.Design.IntegrationTests
             Assert.BuildOutputContainsLine(result, $"RazorTasksPath: {expected}");
         }
 
-        [ConditionalFact]
+        [ConditionalFact(Skip = "https://github.com/dotnet/aspnetcore/issues/24427")]
         [OSSkipCondition(OperatingSystems.Linux | OperatingSystems.MacOSX)]
         [InitializeTestProject("SimpleMvc")]
         public async Task IntrospectRazorTasksDllPath_DesktopMsBuild()
diff --git a/src/Security/Authentication/Negotiate/src/NegotiateHandler.cs b/src/Security/Authentication/Negotiate/src/NegotiateHandler.cs
index 0ef6697857..179a85ed0b 100644
--- a/src/Security/Authentication/Negotiate/src/NegotiateHandler.cs
+++ b/src/Security/Authentication/Negotiate/src/NegotiateHandler.cs
@@ -315,7 +315,7 @@ namespace Microsoft.AspNetCore.Authentication.Negotiate
             // things like ClaimsTransformation run per request.
             var identity = _negotiateState.GetIdentity();
             ClaimsPrincipal user;
-            if (identity is WindowsIdentity winIdentity)
+            if (OperatingSystem.IsWindows() && identity is WindowsIdentity winIdentity)
             {
                 user = new WindowsPrincipal(winIdentity);
                 Response.RegisterForDispose(winIdentity);
diff --git a/src/Servers/HttpSys/src/Microsoft.AspNetCore.Server.HttpSys.csproj b/src/Servers/HttpSys/src/Microsoft.AspNetCore.Server.HttpSys.csproj
index 72b994fff3..0ab19cbe78 100644
--- a/src/Servers/HttpSys/src/Microsoft.AspNetCore.Server.HttpSys.csproj
+++ b/src/Servers/HttpSys/src/Microsoft.AspNetCore.Server.HttpSys.csproj
@@ -9,6 +9,9 @@
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <PackageTags>aspnetcore;weblistener;httpsys</PackageTags>
     <IsPackable>false</IsPackable>
+
+    <!-- Ignore platform compatibility warnings for this project. We know this only works on windows.-->
+    <NoWarn>$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Servers/HttpSys/src/WebHostBuilderHttpSysExtensions.cs b/src/Servers/HttpSys/src/WebHostBuilderHttpSysExtensions.cs
index f7c2b9445f..72ac78b014 100644
--- a/src/Servers/HttpSys/src/WebHostBuilderHttpSysExtensions.cs
+++ b/src/Servers/HttpSys/src/WebHostBuilderHttpSysExtensions.cs
@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Runtime.Versioning;
 using Microsoft.AspNetCore.Hosting.Server;
 using Microsoft.AspNetCore.Server.HttpSys;
 using Microsoft.Extensions.DependencyInjection;
@@ -11,7 +12,7 @@ namespace Microsoft.AspNetCore.Hosting
 {
     /// <summary>
     /// Provides extensions method to use Http.sys as the server for the web host.
-    /// </summary>    
+    /// </summary>
     public static class WebHostBuilderHttpSysExtensions
     {
         /// <summary>
@@ -23,6 +24,7 @@ namespace Microsoft.AspNetCore.Hosting
         /// <returns>
         /// A reference to the <see cref="IWebHostBuilder" /> parameter object.
         /// </returns>
+        [SupportedOSPlatform("windows")]
         public static IWebHostBuilder UseHttpSys(this IWebHostBuilder hostBuilder)
         {
             return hostBuilder.ConfigureServices(services => {
@@ -52,6 +54,7 @@ namespace Microsoft.AspNetCore.Hosting
         /// <returns>
         /// A reference to the <see cref="IWebHostBuilder" /> parameter object.
         /// </returns>
+        [SupportedOSPlatform("windows")]
         public static IWebHostBuilder UseHttpSys(this IWebHostBuilder hostBuilder, Action<HttpSysOptions> options)
         {
             return hostBuilder.UseHttpSys().ConfigureServices(services =>
diff --git a/src/Servers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj b/src/Servers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj
index d262f5cd0b..5727a00650 100644
--- a/src/Servers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj
+++ b/src/Servers/IIS/IIS/src/Microsoft.AspNetCore.Server.IIS.csproj
@@ -11,12 +11,15 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <NativeAssetsTargetFramework>$(DefaultNetCoreTargetFramework)</NativeAssetsTargetFramework>
     <IsPackable>false</IsPackable>
+
+    <!-- Ignore platform compatibility warnings for this project. We know this only works on windows.-->
+    <NoWarn>$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
     <Compile Include="$(SharedSourceRoot)TypeNameHelper\*.cs" />
     <Compile Include="$(SharedSourceRoot)Buffers.MemoryPool\**\*.cs" LinkBase="Shared\" />
-    <Compile Include="$(SharedSourceRoot)HttpSys\**\*.cs" LinkBase="Shared\"/>
+    <Compile Include="$(SharedSourceRoot)HttpSys\**\*.cs" LinkBase="Shared\" />
     <Compile Include="$(SharedSourceRoot)StackTrace\**\*.cs" LinkBase="Shared\" />
     <Compile Include="$(SharedSourceRoot)RazorViews\*.cs" LinkBase="Shared\" />
     <Compile Include="$(SharedSourceRoot)ErrorPage\*.cs" LinkBase="Shared\" />
diff --git a/src/Servers/IIS/IISIntegration/src/Microsoft.AspNetCore.Server.IISIntegration.csproj b/src/Servers/IIS/IISIntegration/src/Microsoft.AspNetCore.Server.IISIntegration.csproj
index addaf56ff2..0c1e8fb171 100644
--- a/src/Servers/IIS/IISIntegration/src/Microsoft.AspNetCore.Server.IISIntegration.csproj
+++ b/src/Servers/IIS/IISIntegration/src/Microsoft.AspNetCore.Server.IISIntegration.csproj
@@ -9,6 +9,9 @@
     <PackageTags>aspnetcore;iis</PackageTags>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPackable>false</IsPackable>
+
+    <!-- Ignore platform compatibility warnings for this project. We know this only works on windows.-->
+    <NoWarn>$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/Servers/IIS/IntegrationTesting.IIS/src/Microsoft.AspNetCore.Server.IntegrationTesting.IIS.csproj b/src/Servers/IIS/IntegrationTesting.IIS/src/Microsoft.AspNetCore.Server.IntegrationTesting.IIS.csproj
index d98aab50da..148e9db98e 100644
--- a/src/Servers/IIS/IntegrationTesting.IIS/src/Microsoft.AspNetCore.Server.IntegrationTesting.IIS.csproj
+++ b/src/Servers/IIS/IntegrationTesting.IIS/src/Microsoft.AspNetCore.Server.IntegrationTesting.IIS.csproj
@@ -20,6 +20,8 @@
       about this structure
     -->
     <NoWarn>$(NoWarn);NU5100</NoWarn>
+    <!-- Ignore platform compatibility analyzer warnings for test and test infrastructure -->
+    <NoWarn>$(NoWarn);CA1416</NoWarn>
   </PropertyGroup>
 
   <Import Project="..\..\build\assets.props" />
diff --git a/src/Servers/Kestrel/stress/Program.cs b/src/Servers/Kestrel/stress/Program.cs
index c962d5bfd7..2a07813d71 100644
--- a/src/Servers/Kestrel/stress/Program.cs
+++ b/src/Servers/Kestrel/stress/Program.cs
@@ -646,7 +646,7 @@ public class Program
         {
             await stream.WriteAsync(new byte[] { 1, 2, 3 });
 
-            var tcs = new TaskCompletionSource<bool>(TaskContinuationOptions.RunContinuationsAsynchronously);
+            var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
             using (_cancellationToken.Register(() => tcs.SetResult(true)))
             {
                 await tcs.Task.ConfigureAwait(false);
diff --git a/src/Shared/CertificateGeneration/CertificateManager.cs b/src/Shared/CertificateGeneration/CertificateManager.cs
index b5c0d0088e..8ad2e14749 100644
--- a/src/Shared/CertificateGeneration/CertificateManager.cs
+++ b/src/Shared/CertificateGeneration/CertificateManager.cs
@@ -28,7 +28,9 @@ namespace Microsoft.AspNetCore.Certificates.Generation
         public const int RSAMinimumKeySizeInBits = 2048;
 
         public static CertificateManager Instance { get; } = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ?
+#pragma warning disable CA1416 // Validate platform compatibility
             new WindowsCertificateManager() :
+#pragma warning restore CA1416 // Validate platform compatibility
             RuntimeInformation.IsOSPlatform(OSPlatform.OSX) ?
                 new MacOSCertificateManager() as CertificateManager :
                 new UnixCertificateManager();
diff --git a/src/Shared/CertificateGeneration/WindowsCertificateManager.cs b/src/Shared/CertificateGeneration/WindowsCertificateManager.cs
index cbeed665d2..e9fe0ef2e1 100644
--- a/src/Shared/CertificateGeneration/WindowsCertificateManager.cs
+++ b/src/Shared/CertificateGeneration/WindowsCertificateManager.cs
@@ -1,11 +1,13 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Runtime.Versioning;
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
 
 namespace Microsoft.AspNetCore.Certificates.Generation
 {
+    [SupportedOSPlatform("windows")]
     internal class WindowsCertificateManager : CertificateManager
     {
         private const int UserCancelledErrorCode = 1223;
diff --git a/src/Shared/PlatformAttributes.cs b/src/Shared/PlatformAttributes.cs
new file mode 100644
index 0000000000..0d44154118
--- /dev/null
+++ b/src/Shared/PlatformAttributes.cs
@@ -0,0 +1,107 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+// Copied from https://raw.githubusercontent.com/dotnet/runtime/b45ee9d37afec0c88141053e86ccf71c6f283000/src/libraries/System.Private.CoreLib/src/System/Runtime/Versioning/PlatformAttributes.cs
+
+#nullable enable
+namespace System.Runtime.Versioning
+{
+    /// <summary>
+    /// Base type for all platform-specific API attributes.
+    /// </summary>
+#pragma warning disable CS3015 // Type has no accessible constructors which use only CLS-compliant types
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        abstract class OSPlatformAttribute : Attribute
+#pragma warning restore CS3015
+    {
+        private protected OSPlatformAttribute(string platformName)
+        {
+            PlatformName = platformName;
+        }
+        public string PlatformName { get; }
+    }
+
+    /// <summary>
+    /// Records the platform that the project targeted.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Assembly,
+                    AllowMultiple = false, Inherited = false)]
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        sealed class TargetPlatformAttribute : OSPlatformAttribute
+    {
+        public TargetPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Records the operating system (and minimum version) that supports an API. Multiple attributes can be
+    /// applied to indicate support on multiple operating systems.
+    /// </summary>
+    /// <remarks>
+    /// Callers can apply a <see cref="System.Runtime.Versioning.SupportedOSPlatformAttribute " />
+    /// or use guards to prevent calls to APIs on unsupported operating systems.
+    ///
+    /// A given platform should only be specified once.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Assembly |
+                    AttributeTargets.Class |
+                    AttributeTargets.Constructor |
+                    AttributeTargets.Enum |
+                    AttributeTargets.Event |
+                    AttributeTargets.Field |
+                    AttributeTargets.Method |
+                    AttributeTargets.Module |
+                    AttributeTargets.Property |
+                    AttributeTargets.Struct,
+                    AllowMultiple = true, Inherited = false)]
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        sealed class SupportedOSPlatformAttribute  : OSPlatformAttribute
+    {
+        public SupportedOSPlatformAttribute (string platformName) : base(platformName)
+        {
+        }
+    }
+
+    /// <summary>
+    /// Marks APIs that were removed in a given operating system version.
+    /// </summary>
+    /// <remarks>
+    /// Primarily used by OS bindings to indicate APIs that are only available in
+    /// earlier versions.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Assembly |
+                    AttributeTargets.Class |
+                    AttributeTargets.Constructor |
+                    AttributeTargets.Enum |
+                    AttributeTargets.Event |
+                    AttributeTargets.Field |
+                    AttributeTargets.Method |
+                    AttributeTargets.Module |
+                    AttributeTargets.Property |
+                    AttributeTargets.Struct,
+                    AllowMultiple = true, Inherited = false)]
+#if SYSTEM_PRIVATE_CORELIB
+    public
+#else
+    internal
+#endif
+        sealed class UnsupportedOSPlatformAttribute : OSPlatformAttribute
+    {
+        public UnsupportedOSPlatformAttribute(string platformName) : base(platformName)
+        {
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/Shared/test/Shared.Tests/runtime/Http2/HPackIntegerTest.cs b/src/Shared/test/Shared.Tests/runtime/Http2/HPackIntegerTest.cs
index 98938a776b..704dad8ac4 100644
--- a/src/Shared/test/Shared.Tests/runtime/Http2/HPackIntegerTest.cs
+++ b/src/Shared/test/Shared.Tests/runtime/Http2/HPackIntegerTest.cs
@@ -55,12 +55,13 @@ namespace System.Net.Http.Unit.Tests.HPack
         public void IntegerEncoderDecoderRoundtrips()
         {
             IntegerDecoder decoder = new IntegerDecoder();
+            Span<byte> integerBytes = stackalloc byte[5];
 
             for (int i = 0; i < 2048; ++i)
             {
                 for (int prefixLength = 1; prefixLength <= 8; ++prefixLength)
                 {
-                    Span<byte> integerBytes = stackalloc byte[5];
+                    integerBytes.Clear();
                     Assert.True(IntegerEncoder.Encode(i, prefixLength, integerBytes, out int length));
 
                     bool decodeResult = decoder.BeginTryDecode(integerBytes[0], prefixLength, out int intResult);
diff --git a/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs b/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs
index d20503d63e..7134abc1f9 100644
--- a/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs
+++ b/src/SignalR/common/Http.Connections/src/Internal/HttpConnectionDispatcher.cs
@@ -580,7 +580,7 @@ namespace Microsoft.AspNetCore.Http.Connections.Internal
             if (oldContext.User.Identity is WindowsIdentity windowsIdentity)
             {
                 var skipFirstIdentity = false;
-                if (oldContext.User is WindowsPrincipal)
+                if (OperatingSystem.IsWindows() && oldContext.User is WindowsPrincipal)
                 {
                     // We want to explicitly create a WindowsPrincipal instead of a ClaimsPrincipal
                     // so methods that WindowsPrincipal overrides like 'IsInRole', work as expected.