[2023] CK3 shuts my PC down mid-game

Please update that nVidia driver to June 2023 https://www.nvidia.com/Download/index.aspx?lang=en-us

THEN 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 that help?  

You shouldn't be getting temps like that at 60; what fps are you seeing in the game now? If it is more than 60 check you set that cap AND disabled Vsync.