For anyone moving a WPF app over to WinUI 3 and getting tripped up by the API differences, Ive been working on a reference page that maps it out. It lays out the common WPF APIs and XAML patterns side by side with their WinUI 3 equivalents, with notes on the spots where the swap isn't 1:1.

Not exhaustive yet. I’m still adding to it. If you’ve run into something that isn’t listed, drop it in the comments and I’ll add it. The docs are also open to PR

WPF to WinUI XAML Equivalents Reference