Kelsonk Hmm yeah, I do use the gestures for the system commands on my Pixel for testing. At least with our app setup, those gestures (swipe up to close, swipe from side to go back) do not work normally within the app as long as it's in Immersive Mode. Instead, swiping from any edge will bring up the Android UI, and you have to swipe a second time to actually use one of the gestures -- or just tap in the center of the screen to go back into Immersive Mode.
So I guess it doesn't really disable the gestures (I wonder if that's actually possible with Android on an app-by-app basis?), it just makes it a two-step process for players to confirm they actually wanted to exit the app.