It is already possible to run Felgo apps and games with or without the top status-bar (see Theme.colors.statusBarStyle).
We generally do not hide the android bottom navigation, as we recommend to also allow the usage of e.g. the back-button for devices with no hardware button. Otherwise developers might design apps that depend on the button and are not aware that it might not be available on certain devices then. So its good to not hide it to provide the same navigation possibilities across devices.
For more information how to manually add immersive fullscreen mode on Android see this topic: