iOS.SystemGestureDeferMode deferSystemGesturesMode is more confusing than it is helpful.
What works better is to have a small border around the app that ignores input. This allows system gestures to function without also triggering game input. The problem is that both the system gestures and the game input are being triggered at the same time, not that one needs to behave like your phone is broken and then trigger game input anyway.
To make matters worse, Android phones also have system gestures that trigger from the edges but no effort has been made to help Android developers with this issue.