if we change the default to hide the UI, then it would also do that on larger devices,
Understood. Let's keep it as an option. I think the majority of Interstellar users would be on mobile.
Do other apps have back gestures as well?
It really depends on the app. I use Voyager and it supports back gestures everywhere.
IMO, back gestures should be handled by the OS
Unfortunately iOS handles back gestures differently. The problem is that without back gesture I need to tap the upper left corner every time I want to go back. With huge phones these days I have to use two hands to operate it.
PieFed webapp supports back gesture (via Safari), and it remains my app of choice for this reason.
You need to open a restaurant.