Re: Camera rotation broken in Sims 4
@Blackbird0318 An overlay is a user interface for an application that sits over the top of another app. It's typically transparent to some degree, and it's most often used for gaming, where you might want to see other information without having a second window open. Most or perhaps all game launchers have an overlay, the EA App and Steam included, as do some other apps like Discord that people might want to interact with while gaming.
The EA App in-game overlay can be toggled under Settings > Application. Steam's can be disabled in settings as well. Discord's won't be active if Discord itself isn't running, but make sure it's not running in the background. The same goes for other apps: if they're not running, neither is their overlay.