[2023] Line down screen causes shadows on the right to disappear.

I take it that second video adapter is an integrated Intel one, as its common? What you could do is enable it again and connect the monitor to that, see if it still happens.

And, unload GeForce Experience before starting the game, if it is running.

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.

Does your monitor support G sync or any of that kind of function? If so what is its setting in that regard?


Any of those make any difference?