For anyone else running into this issue, in my case at least (developed in Swift and using storyboard), after using the Xcode tool to migrate to a single app, I needed to go into the storyboard and change the Module for every interface controller and row controller I had created. These still specified the watch app extension rather than the watch app.

I finally got to the point where I used Xcodes's process to upgrade my app from an extension to a single app. Once I did, the app crashes during the launch process with a signal SIGABRT error pointing to : class ApplicationDelegate: NSObject, WKApplicationFelegate (I renamed the class from ExtensionDelegate) with no indication of it having been a particular line of code that led to it. Just a general question, were there any other obvious changes that needed to be made for this to work?

Thanks for the details, I see the option there. I have the same concern about whether the old extension format apps re no longer supported. Apple documentation doesn't appear to have been updated for Xcode 15 in regards to creating a phone app with a companion watch app. The steps involved in are quite different and, from what I can see, such apps are now created with a single watch app target. And forgive me if this question is slightly off topic, but has anyone else also seen their watch apps being inexplicably terminated?

Thanks for the update. Can you please indicate where in Xcode to find the process you mentioned (to upgrade a watch app from an extension to a single app)?

Were you able to resolve the issue? I'm experiencing similar behaviour running the release version of watchOS 10 (and 10.0.1).