As mentioned in Stack Overflow, try Force Quit Application when XCode is running. option + command + esc Restarting XCode didn't work for me, but forcing it to quit did.

Same assert with iOS 13.0. I stepped through the code and TARGET_OS_SIMULATOR and TARGET_IOS defines are set.

Correction to the above: I tried the simulators iphone 11, 12 and iPad Gen 9 with iOS 15.4 I'm downloading the iOS 13.0 to try next.