Should be the default in my opinion.
The problem with that is that Interstellar is not only available on phones, but also on large tablets and desktop devices. So if we change the default to hide the UI, then it would also do that on larger devices, which is probably unwanted.
What we really need is an onboarding process / welcome screen, which would ask you to configure some common settings and add your first account.
Will you consider adding back gesture?
Possibly? Do other apps have back gestures as well? The problem here is if I added back gestures from post back to Feed, then would people expect it to work the same for all pages (like community page back to Explore, user back to user comment, etc.)? It seems like it would be quite a bit of effort to implement for all of those.
Additionally, it seems like having that back gesture would rule out having the possibility of feed swiping (being able to swipe on one post to get to the next) in the future.
IMO, back gestures should be handled by the OS, as if you swipe from the side out on Android, then it goes back one screen, and that's handled by the Android OS.
I'm not ruling it out, but I do want to get more feedback on the idea.