The problem is still there (Xcode 16.2, MacOS 15.3.2). As far as I can tell, it occurs when the same custom font is both distributed in the catalyst app and also installed on Mac. The app runs on under Mac Catalyst from Xcode, but the generated app will not open on Mac. A workaround is to disable the custom font on Mac in Font Book (or remove it)

I have reported as FB16864964