There is nothing in the upper corner. Also swiping up doesn't do anything
25 days ago(+1)
The HUD is hidden during dialogues. It appears when the dialogue ends.
I won't be able to tell you about the "back" button - it all depends on your device type.
For me, it's a swipe from the bottom (in portrait mode) and the "minimize" and "back" buttons appear there. The "back" button will open the menu even during dialogue.