finkleroy: I'm not doing either of those things, and this is the only game that has tearing.
kingarepa: Forcing Vsync to ON and turning turning OFF triple buffering didn't work for me either. I could still see the big tear in the middle of the screen. However, it worked after I added one additional step. I downloaded the widescreen fix at this link:
https://thirteenag.github.io/wfp#callofcthulhu After extracting the Engine folder and placing it in my GOG Cthulhu directory "C:\Program Files (x86)\GOG Galaxy\Games\Call of Cthulhu", I started the game and the screen tear disappeared. I'm now able to run the game at 1920X1080 or 3840X2160.
I still have Vsyn forced to ON in the Nvidia Control panel and triple buffering set to OFF. I don't know if that matters.
Does your diary reading @ 3840x2160 look like this?:
https://github.com/ThirteenAG/WidescreenFixesPack/issues/420 I can run the game, too, at 3840x2160, but the diary looks like it does in the link above, unfortunately. So I dropped down to 2560x1440 to get a proper diary read.
I don't have a nVidia card, but an AMD card, and run the game with Vsync off but with Enhanced Sync turned on in the drivers--provides ~90% of the frame-rate of vsync off but with little to no tearing.