Extras/other people in the background are acceptable to meet the criteria but ideally with no human/entity on the screen at all that isn’t played by the same actor.

Movies like ‘Men’, ‘Moon’ or ‘The Nutty Professor’ don’t meet this criteria for example, due to the exceptions of characters played by other actors.

And it has to be somewhat mainstream and not a low budget student film or something.

Edit: I also meant that they play multiple characters…