If one’s retired, does not mean that one has more time…
Due to several projects, I found the time to update all of my iOS devices some days ago
→ The solution for my document-based Swift/SwiftUI application turned out to be that simple (Why did I get no answer from the Apple forums?):
→ just update Your devices, after updating, ALL of my document-based app’s are working, not one problem (beside of the app-icon color). The updater does so many things behind the scenes..