I only mentioned Steam because I've had an experience where that happened to someone. They were running some game (similar to Jackbox but it wasn't that) for a conference and were just outputting the display and the Steam update prompt showed up on top of the display. It wasn't a big deal, it was just an example that summed up exactly the types of things I'm talking about.

And no, this wasn't a Steam overlay. It was a prompt to restart the Steam app to complete some update. That does not need additional permissions.