Following the workspace switch.

[c-bata]

Cocoa API is here:
https://developer.apple.com/reference/foundation/nsnotification.name/1527073-nsworkspaceactivespacedidchange

Maybe it is easy to develop macOS native application using swift.
https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/CocoaViewsGuide/Introduction/Introduction.html