I also have the same issue with a few users. Maybe it's related to the general StoreKit 2 issues, such as the StoreKit 2 testing framework broken in 26.4 (also verified known issue by Apple). This seems to be already fixed in 26.5 so that gives me hope that maybe this issue will also be fixed in 26.5.

Any news on this topic?

It would be great if there was a setting to turn off this check as a developer, maybe like the developer mode on iOS.

I have a Mac Catalyst app with a menu bar extension. The menu bar extension is a regular Mac app integrated in the Catalyst app with the bridging header. Both apps use app groups for communication. The problem is that I still get the error described above, even though the app group is declared in the entitlements of both apps. If the app is downloaded from App Store, it does appear to work normal. But the problem makes development really annoying, and it also happens with TestFlight. Does anyone have the same problem?