I had the same issue only could change to Full screen after prologue finished ie after you kill all the NPC adds and Boss and learn the basic combat buttons.
It will then start you in a village, start of the story campaign, at this point you can go to options and change display, resolution etc... I'm now running at Full screen 4k 60fps
3840x 2160.

I think it may be a bug at start, as l couldn't make the window any larger, just played as is until it jumped to new scene. Hope that helps..

Originally posted by mdkmax_99:

I had the same issue only could change to Full screen after prologue finished ie after you kill all the NPC adds and Boss and learn the basic combat buttons.
It will then start you in a village, start of the story campaign, at this point you can go to options and change display, resolution etc... I'm now running at Full screen 4k 60fps
3840x 2160.

I think it may be a bug at start, as l couldn't make the window any larger, just played as is until it jumped to new scene. Hope that helps..

Thanks a bunch! Once I got to the first village the in game menu didn't work but I was able to change the resolution in the Special K menu.

For anyone finding this late like I did, I fixed it this way (by accident), without having to play any part of the game:

1) Set the display settings as I desire.
2) Started a new game for the first time.
-- During his whole time; the game is confined within a "non-full-screen" rectangle that is smaller than my screen, with my desktop on the left out parts. --
3) A cutscene started playing, still with the silly non-full-screen thing.
4) Immediately alt+F4'ed to quit out of the game.
5) Restarted the game.

It was then full screen as normal (also with the Radeon Super Resolution upscaling from 1224p to 1440p, just like I had set it).