If you exit the Steam app entirely and run ck3.exe directly , what happens?
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/Stellaris/settings.txt and pdx_settings.txt .
From your Documents/Paradox Interactive/Stellaris/logs/ folder, attach system.log , error.log .
In this folder are some .log files:
C:/users/<UserName>/AppData/Local/Paradox Interactive/launcher-v2/
Please attach them here.