[s]I reset win10 and installed the new AMD drivers and fullscreen works when I first launch the game, but after I alt-tab it switches to windowed. It doesn't really run in a window though because it still takes a while to alt-tab. however, my brightness settings do not change after alt-tabbing back in, similar to running in windowed. Also, I can still see the game running when holding alt tab which normally doesn't happen[/s]

fixed by disabling game bar in xbox app