Catalyst example using an AppKit-provided NSVisualEffectView to provide a translucent blurred window
CatalystEffectViewChrome
This project demonstrates how to insert an NSVisualEffectView to the root of the main window of your Mac Catalyst app, to provide a translucent window background effect in a more-robust way than my other sample.
The window contents can be provided by UIKit or SwiftUI (as in this example).