Contribute to the Maui backend for GTK and/or Qt, nothing is stopping you

Alternatively, just because you're on .NET doesn't mean you need to use Microsoft sanctioned UI toolkits, just as C++ has no "official" UI toolkit. You're free to pick up some GTK or Qt bindings if you want a native feeling and your application is already architectures correctly. Alternatively, throw Imgui at it if you just need dev tooling, or maybe try other cross platform toolkits in the ecosystem like Avalonia or Uno