I'm also struggling with porting a document-based, scene-based iPad app to the Mac with Mac Catalyst. I've been struggling with the same problem as DavidNZ. When I double click in Finder to open a document sometimes it opens, and sometimes just a blank window opens. Same with the Open Recent menu item. Sometimes it works and sometimes it doesn't. I have a feeling this is a threading issue, but I'm not sure what needs to be done asynchronously in my code to make it work. I can also confirm the issue with Cmd-Q vs selecting Quit from the menu. In the first case changes aren't saved, but they are with the second. I'll try updating the change count on viewDidDisappear or one of the other lifecycle events to fix this, but it really seems to be a bug in catalyst. I think I bit off more than I can chew here. I'm tempted to copy the code base and eliminate scenes, or painfully duplicate the app in AppKit. Ugh.