I just ran into the same problem. During early development I have disabled the launch schreen and then wanted to add it back to my project after allowing split screen usage etc. I did this the way Xcode usually would offer it: use the drop down menu to select the LaunchScreen file. But it ends up including the file extension in a "basename" field. Actually it is a bug in Xcode. When selecting the storyboard file, the file extension shall get removed. Obviously this bug already has quite some age.

Well - not everyone wants to use Swift - why no Objective-C implementation? (Well I will have to use nw_browser_t then)

This issue seems to be related to TabViews, not to SwiftUI or NavigationView. I have seen this in my Xcode debug output in an app written in Objective-C and without Navigation View - except I got "(response-not-possible)" instead of "(null)".