Make sure you set your game to run Full Screen Borderless / Windowed. ADS runs as a top level window and if your game is running in Exclusive Full Screen mode, no other apps can operate above the game view.

On older hardware this was true, but with today’s machinery there is no difference in game speed or performance. I’ve personally been running in Full Screen Borderless mode with Call of Duty and Fortnite for 5+yrs and have never experienced a difference in performance.

Nope - it’s neither. It’s no different than putting scotch tape on your screen and drawing a dot in the middle, or a smudge of toothpaste to find center. It’s your monitor, you can do whatever you want with it. This is, essentially, a tape simulator.