Galaxy S9+ navigation bar settings (shall fade out instead of being permanent)


The navigation bar of the S9+ (of my girlfriends) does not disappear, but remains permanently at the bottom.

Has anyone managed to make it disappear (as one would expect)?

a) with on-board means?
b) with an additional app? (have found: Navigation Bar for Android, in the PlayStore).

Thanks for your help!

What about -->settings -->system -->button ?