I was able to press ALT+ENTER to switch to windowed then ALT+ENTER again to make it fullscreen.
Found settings on left and changed resolution to 4k.
Maybe the bug is because I have 200% scaling set in Windows? No idea.

Hmm, can’t say if that was the actual cause in your case, but yeah (I’m also always playing in 4K and Win 10), in my experience Unity games (that mostly use borderless windowed mode) indeed often clash with the Windows scaling (e.g. with 200%). At least that happened to me as well, with quite a lot of games and always different bugs/results. So meanwhile I’m always using the 100% scaling before starting any game just to be safe, and always turn my desktop to the resolution that I want to play the game in (Unity adjusts much better then). But whatever the cause, I’m glad you could solve your problem :)