These 2 steps should fix the black screen issue:
Otherwise, once you’ve put your Fractured But Whole into a window, you can either keep playing in windowed mode (I wouldn’t) or you can navigate to “Options”, then into “Display” then “Window Mode” and finally pick “Windowed Fullscreen”, now you’re basically playing in fullscreen. If you’re comfortable playing in a window, then that’s all you really need to do. It’s a really simple fix, all you have to do is put the game into windowed mode by hitting “alt + enter”. Since that really sucks, I’m going to show you how to temporarily fix it.
Since South Park: The Fractured But Whole released, a lot of us who are trying to play it on PC have been experiencing issues with a black screen upon launch.
