One of my favorite features is "Move & Resize Windows" with modifiers so I don't have to find the borders..
A known limitation is that this does not work with all windows:
I'm a developer myself and learned that this is the case for (all?) apps created with DotNet/AvaloniaUI.
Probably a question for @Andreas_Hegenberg: do you know what I could do in my own apps to make the main window react in the right way? In the linked post you mentioned APIs that are not properly implemented in those apps. What are those?
Most important would be that the windows have the size and position attributes gettable and settable (default for any standard NSWindows, not sure how windows are created with DotNet/Avalonia.