I have a .netcore3 [console] app in the form of a DLL, which uses the uap xaml APIs that allow creating xaml objects, etc (Windows.UI.Xaml.Hosting, etc.).

When I run the app, I get an exception:
Unhandled Exception: System.Exception: Catastrophic failure

WindowsXamlManager and DesktopWindowXamlSource are supported for apps targeting Windows version 10.0.18226.0 and later. Please check either the application manifest or package manifest and ensure the MaxTestedVersion property is updated.

Since the hosting feature requires an app manifest, I wrote one, but nothing in the build process is picking it up (I just put garbage into the manifest and nothing complained). I figured that since my app is a DLL and not an exe, maybe the manifest thing doesn't work.

I found this issue talking about app.manifest in dotnetcore3 but not clear what the fix is for the MaxTestedVersion issue I'm seeing is.
#1899