Attempting:
xcrun simctl
in terminal
yields:
xcrun: error: unable to find utility \"simctl\", not a de
I had the same problem. My application was working well but suddenly in next run, it started throwing the "simctl" error. It seems I had started Xcode update installation in the background.
Fix: I just started the Xcode application and it prompted to install some pending tools update. After Xcode updates, my app started working normally.
In Xcode, open the Xcode menu at the top, then select Preferences…, and then select the Locations tab.