I am on an ARM Mac (M4). The SDK 2 simulator offered an option for full screen, which was great for previewing games. The option seems to have been lost in the move to SDK 3:
Rae suggested in Discord that this was a potential consequence of the simulator codebases being merged. Regardless of the reason for the regression, I wanted to put in an official request for full screen mode to be restored to the macOS simulator in a future release 
P.S. Thanks to everyone at Panic for making and maintaining this great system!