I just had the same issue - I built a simple intent handler without an app extension and kept getting this error. It turns out that the project must NOT have "Siri" added in the Capabilities section. Remove it and it'll start working

Still getting this same problem with Xcode 15.0.1, just added a new Widget Extension target, made no changes - starting with a fresh app sounds insane as my app is huge...

This would be great for my ride tracking app. When the user starts a ride it's annoying to have to start the app on the watch manually. Hoping this feature will be added soon.