I was finally able to isolate my hang issue to a simple app for submission of a feedback ticket and it turns out it was not even related to Core Data in my case. In my case, the hang was happening when I had a generic destination view and a generic wrapper struct for the inner NavigationLink item combined with also using an @AppStorage in that generic destination view as well. Oddly enough, either removing the @AppStorage or changing the wrapper struct to use a concrete type fixed it for me!

Now I see that specifically turning off the "Thread Performance Checker" checkbox under Run Diagnostics in the scheme fixes it for me and I can leave both the Debug executable and Main Thread Checker turned on.

I should add that the selected App Group displayed under Signing & Capabilities in Xcode is now shown in red. It doesn't seem to result in a real problem yet though. Crossing fingers that it doesn't cause my release build to fail or app store submittal to fail though.

I just filed FB15694000 as well. This is a pretty serious regression bug, IMO. It's probably breaking sidebar navigation for all existing Mac production App Store apps that use sidebarAdaptable TabViews in 15.1 even if they worked fine in 15.0! Hopefully users will figure out they can tap on the empty space around the text to get it to work but I'm sure glad my app has not been released yet! 😅

Never mind, I just confirmed it is indeed fixed in 15.2 beta 2!