over 2 years ago - AndrewT - Direct link
When you run the ck3.x64 executable form the terminal command line, what output do you see?

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

Also in Steam please click on Steam-Help-System Info, and paste everything there into a text file and attach that here.  
over 2 years ago - AndrewT - Direct link
Right click on this game in your Steam Library, manage, browse local files. Open up the binaries folder, the ck3.x64 is in there.

In the terminal session navigate to that folder then do:
./ck3.64