Fixes required now MSBuild.Extras.SDK has gone

Rx.NET/Source/src/System.Reactive.For.Uwp/Strings_PlatformServices.Designer.cs

@@ -40,7 +40,7 @@ namespace System.Reactive.Uwp {
         internal static global::System.Resources.ResourceManager ResourceManager {
             get {
                 if (object.ReferenceEquals(resourceMan, null)) {
-                    global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("System.Reactive.For.Uwp.Strings_PlatformServices", typeof(Strings_PlatformServices).GetTypeInfo().Assembly);
+                    global::System.Resources.ResourceManager temp = new global::System.Resources.ResourceManager("System.Reactive.Uwp.Strings_PlatformServices", typeof(Strings_PlatformServices).GetTypeInfo().Assembly);
                     resourceMan = temp;
                 }
                 return resourceMan;

Rx.NET/Source/src/System.Reactive.For.Uwp/System.Reactive.For.Uwp.csproj

@@ -1,7 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>uap10.0.18362</TargetFramework>
+    <!-- Note: our workaround for the lack of uap10.0.xxxxx support requires use of TargetFrameworks (plural)
+    even when there's just a single target. -->
+    <TargetFrameworks>uap10.0.18362</TargetFrameworks>
+    <RootNamespace>System.Reactive.Uwp</RootNamespace>
 
   <PackageTags>Rx;Reactive;Extensions;Observable;LINQ;Events;Windows Forms</PackageTags>
     <Description>Reactive Extensions (Rx) for .NET</Description>
@@ -13,6 +16,10 @@
     <Nullable>enable</Nullable>    
   </PropertyGroup>
 
+  <ItemGroup>
+    <ReferencePath Include="$(TargetPlatformSdkPath)UnionMetadata\10.0.18362.0\Windows.winmd" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Include="..\AssemblyInfo.cs" Link="Properties\AssemblyInfo.cs" />
     <Compile Include="..\System.Reactive.For.WindowsRuntime\AsyncInfoExtensions.cs" Link="AsyncInfoExtensions.cs" />

Rx.NET/Source/src/System.Reactive.For.WindowsRuntime/System.Reactive.For.WindowsRuntime.csproj

@@ -29,6 +29,10 @@
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
+  <ItemGroup Condition="'$(TargetFramework)'=='uap10.0.18362'">
+    <ReferencePath Include="$(TargetPlatformSdkPath)UnionMetadata\10.0.19041.0\Windows.winmd" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Include="..\AssemblyInfo.cs" Link="Properties\AssemblyInfo.cs" />
   </ItemGroup>

Rx.NET/Source/tests/Tests.System.Reactive/Tests.System.Reactive.csproj

@@ -37,7 +37,7 @@
     <ProjectReference Include="..\..\src\Microsoft.Reactive.Testing\Microsoft.Reactive.Testing.csproj" />
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'net472' or $(TargetFramework.StartsWith('net6.0-windows')) or $(TargetFramework.StartsWith('net8.0-windows'))">
+  <ItemGroup Condition="'$(TargetFramework)' == 'net472' or $(TargetFramework.StartsWith('net8.0-windows')) or $(TargetFramework.StartsWith('net9.0-windows'))">
     <ProjectReference Include="..\..\src\System.Reactive.For.WindowsForms\System.Reactive.For.WindowsForms.csproj" />
     <ProjectReference Include="..\..\src\System.Reactive.For.Wpf\System.Reactive.For.Wpf.csproj" />
     <PackageReference Update="coverlet.collector" Version="6.0.2">