I tried the preview version of Rx and it seems that System.Reactive.Concurrency.DispatcherScheduler.Current is not available for WPF net5.0 RC1. For NetCoreApp 3.1 it works correctly.

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">

  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFrameworks>net5.0-windows;netcoreapp3.1</TargetFrameworks>
    <UseWPF>true</UseWPF>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="System.Reactive" Version="5.0.0-preview.16" />
  </ItemGroup>

</Project>

Based on this commit the HAS_WPF constant should be defined: db8e159

My dotnet version is 5.0.100-rc.1.20452.10. I'm using VS 16.8.0 Preview 3.1.

What am I doing wrong?

Thank you Tomas