OBS doesn't take over. It's just another app. What did you expect?
You're literally broadcasting your PC. So don't have anything on your PC that you don't want to show! If that means a dedicated PC for broadcast, instead of your main one with a hundred apps all open at the same time because you never clean up (I've seen people like that), then so be it.
Maybe a separate account would be enough, instead of a separate PC, but you get the idea. Or just keep it clean. Close (don't minimize) what you're not using, etc.