What was the nature of the upgrade?
I take it that was attempting to deal with the startup issue in your other thread - did it in fact help? I guess it must have, or you couldn't get into the game to have this new problem!
Right click on ck3.exe , properties, compatibility. Tick "disable fullScreen optimisations" untick every other box in that dialog, Apply and exit.
Then in the launcher Game Settings menu, select fullScreen display mode, Vsync off, cap refresh rate at 60.
I take it that was attempting to deal with the startup issue in your other thread - did it in fact help? I guess it must have, or you couldn't get into the game to have this new problem!
Right click on ck3.exe , properties, compatibility. Tick "disable fullScreen optimisations" untick every other box in that dialog, Apply and exit.
Then in the launcher Game Settings menu, select fullScreen display mode, Vsync off, cap refresh rate at 60.