Well, in the window version, you can press H to Hide the UI by default in Ren'Py, but, for Android, you actually have to code it in... ☹
...iirc, you can put this in the menu:
imagebutton auto "gui/quick_menu/load_button_%s.png" action [HideInterface(), Hide("in_game_menu")]
Basically, the HideInterface() hides the window and the Hide() function hides the menu you were in that way this can go in a menu 🤔
...My apologies if that doesn't make sense... 😣