Thank you for your comments! When these problems arise I restart both the iPhone and the Watch, disable Bluetooth in iPhone, physically connect the iPhone to the Mac mini and after the iPhone shows up in Devices I turn on Bluetooth again. It usually did not make a difference. Things would be worse after updating OS in iPhone and Watch. Devices and Simulators would report old watchOS versions, and would not acknowledge apps that are installed in both the iPhone and the Watch.

I experienced the same problem of the original poster. Tried to change the code posted by sam181818, but it still crashes. However, I can build/run Apple's sample code provided with the tutorial, and everything runs. Could this be due to the expected deployment iOS? I'm building while expecting to use iOS 15.2, but Apple's Xcode project is built for iOS 14.0. Thanks for any comments!