Sorry, its not my fault that you are so impolite to not read what a person was writing but answering with untrue nonsense. dont take it personally.
What i was writing: NavBar hiding is working on Android 11 as well as gesture apps.
I am on A11 Oxygen OS on my Oneplus 8, hiding the NavBar with the way described in my link and i am using "edge gesture" for now, as the XDA gesture app is not working.
Fluid Navigation and Ubiki Touch is working as well with that method.
Ubiki is not offering a "force close forground" action, Edge Gesture is not offering multiple Edge Bars but only 1 and FNG is not offering "swipe up/down" "tab" etc actions - thats why i would prefer the XDA application but its force closing.
Even if there wouldnt be a way to hide the navbar it would be always an option to use the gesture control with a visible navbar (like it is working in the other gesture apps) - its not too cool, but functional.
But now, as there is a way to hide the navbar in A11 it would be time for the developer to get the App working again, as there are many paid customers.