It worked well until this afternoon.

I've restarted the computer, checked Steam cache integrity and tried starting it directly from the folder, no success unfortunately.

The log has some suspicious lines about D3D9 and D3D11 initialization failing.

output_log.txt DxDiag.txt

Please note Official publisher customer support is available from  Paradox Interactive at: https://support.paradoxplaza.com/hc/en-us so you may want to submit there as well.