The hidden UI feature is nice, but it takes too long to enable it for something that is turned on and off all the time. I think a 4 finger tap would be a good option for toggling it, it is also the default shortcut in Procreate.
In that case, it would also be a good idea to display a bespoke button for turning it off instead of the Nomad logo, so people don’t panic if they accidentally tap with 4 fingers and suddenly the whole UI is gone (also from Procreate, those guys are really good at making UIs, aren’t they ).