Settings, search for 'draw over', revoke that permission from apps, try again
Go to settings, search for 'display over other apps', try disallowing that for every app.
When that menu is meant to appear as 4th button, but with navigation gestures it doesn't appear at all.
Used this app https://play.google.com/store/apps/details?id=com.irishin.buttonsremapper to remap back button back to back , minecraft doesn't "find"...
Yeah, please disable/remove this "feature", very annoying. https://bugs.mojang.com/browse/MCPE-16951