The most common cause of this game failing to start since the recent 1.14.3 patch is Avast, Norton's, Sophos or AVG antivirus (at least!) blocking the updated ck3.exe . Regardless of what AV app you use, make sure ck3.exe is in all its exceptions lists.
If that's not the case here, or doesn't help, Please do a full
clean re-install:
- move any valued save games elsewhere
- "uninstall" in Steam-CK3
- manually delete both the Steam/SteamApps/common/Crusader Kings 3 AND Documents/Paradox Interactive/Crusader Kings III/ folders - In particular make sure there are no files or folders left under either the Steam CK3 or Documents CK3 locations, before installing again.
- re-install game in Steam, run a Steam Verify when done.
- add CK3.exe to the exceptions list of your antivirus app; ESPECIALLY if you have Windows Defender, add it to the Ransomware "Apps Allowed Through" list.
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.
If those don't help:
DXDIAG is a program you run from the Windows search box on the task bar. After running it will open a window and start collecting info with a progress bar in the lower-left corner. When it completes click the 'save all information' button and save it to a file then attach that file here. IF dxdiag.txt fails to attach here, rename it to dxdiag.log , or zip it up.
Please attach here your Documents/Paradox Interactive/CK3/pdx_settings.txt .
From your Documents/Paradox Interactive/CK3/logs/ folder, attach here system.log , error.log , exceptions.txt