I just noticed that fullscreen exists.
I don't think it's a harmful tag, but not a very useful (not too used either, 10 questions as of writing) one either.
Should we keep it around?
I don't think the tag should go away.
I think that the problem domains of "dealing with fullscreen switches" and "handling 'borderless fullscreen'" and similar are reasonable and on-topic for a game development site. It's possible we should clarify the scope of the tag though.