AvaloniaUI and Uno are pretty great! There is also new actively maintained fork of GtkSharp as well as many other bindings. Honestly, it's as good as it gets in many other alternatives which don't have the advantages of .NET.
It's an important disclaimer as someone might read this and go write another tool in Python + Tkinter (with terrible results).
It's an important disclaimer as someone might read this and go write another tool in Python + Tkinter (with terrible results).