The Navigation Bar problem can be easily solved. I downloaded "Navigation bar remover/activator (root)" from Play Store (https://play.google.com/store/apps/details?id=com.conena.navigation.bar.remover) to enable the on screen nav bar - the fingerprint gestures still work. Then I switched to immersive mode, now I only use the FP gestures and when I need it, I can swipe up to have the nav bar available again.
Enabling the navigation bar also solved e.g. the issue with Titanium Backup showing no menu button...
Enabling the navigation bar also solved e.g. the issue with Titanium Backup showing no menu button...