The best solution would be if the app could handle this itself.
I know when I was compiling my own version (before nightly builds of Android were a thing - an awesome thing by the way!) I made some changes so that firstly it would run in immersive mode and secondly I hijacked the two fingers swipe up and down gestures. I made it so that two fingers swipe down would hide the keyboard if it was showing and two finger swipe up would show the keyboard if only the quick shortcuts were showing. If only the quick shortcuts were showing a two finger swipe down would hide them. If nothing was showing then the first two finger swipe up would show the quick shortcuts then if you swiped up again the keyboard would show. (I also removed the toast when the quick shortcuts were hidden).
I found that this worked really well and allowed me to play in fullscreen without the navigation bar.
I’m not sure if there is anyway something like that can be integrated as it might not suit everyone? It was great for me because obviously screen real-estate is huge when you are talking about a screen that is. 5" - 6".
Also I think that (for me anyway) if fixes some slight issues when scaling fonts. My resolution is 1920px wide (without the navigation bar) but with the navigation bar it’s 1794px and with a font width of 8 it seems to scale perfectly at the full resolution of 1920px but not quite perfectly at 1794px.
