something is taking system focus, is everything minimising, or just games?   honestly sounds like something misbehaving, like, a persistent update or something, check task manager to see what is using a lot of resources. I'm not sure about Overwatch, but I notice that Ubisoft games will minimize if you alt+tab away, but most other games will not. so I'd assume something keeps taking system focus, could even be a print job that is stuck in the printer spooler.

or Services -> Event Viewer so see if… See More