In the game launcher please set Display mode to windowed.
THEN go here:
This article lists the download links for the latest versions of Visual C++.
support.microsoft.com
And run the x86 and x64 installers there.
IF that 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/CK3 AND Documents/Paradox Interactive/CK3 folders
- 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.
- start the game with no mods active and test
In particular make sure there are no files or folders left under either the Steam CK3 or Documents CK3 locations, before installing again.
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.
Please attach your Documents/Paradox Interactive/CK3/pdx_settings.txt .
From your Documents/Paradox Interactive/CK3/logs/ folder, attach system.log , error.log