[2020] Crash on start-up (windows/steam) 1.1.3

With Win 8.1 you probably need to manually install the latest Visual C++ modules. Please go here:
https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads and run the x86 and x64 installers, then reboot.

If that doesn't help, unload the Steam app entirely and run ck3.exe by itself - what happens then? Any error?

And what antivirus app do you use?  

If the game does not create the Documents/paradox/ck3/ folder, or does not populate it, it's probably an antivirus issue. I don't know Trend ata ll, you could check with their support how to ensure the game is fully allowed through it.