[DiabloD3]

That isn't quite right.

Notice how WinUI 3.x is the first thing named publicly named WinUI, but its already at 3? UWP is 2.x, Metro/WinRT/WPF is 1.x. They're all part of the same family of XAML UIs.

The part that got hard killed, and backwards support was absolutely 100% murdered was the Silverlight stuff, which was a XAML predecessor (and RIA runtime to compete with Flash/Air) written entirely in C#. For performance reasons, the WinRT/WPF->UWP->WinUI 3 branch of the family is largely WinRT-dialect C++.

So no, Microsoft actually hasn't abandoned the tech, they abandoned the dumb idea that all apps need to work on the Windows Phone (which no longer exists) and must be released on the Microsoft Store (which now allows apps in other languages), and everything has to be written in C# (which, again, is no longer forced on programmers), and everything needs to be Windows-only (Project Reunion aka MAUI brings both CLR and non-CLR WinUI apps to Linux).

Also, I'm not sure why you're branching WinUI family off from .net, as WinUI is the UI toolkit for CLR apps.