[2021] Game launcher crash

If you can run ck3.exe but the launcher cannot, there will still be a launcher issue of some sort.

What launcher version do you see? Current is 2021.2

In this folder are some .log files:
C:/users//AppData/Local/Paradox Interactive/launcher-v2/
Please attach them here.  

To see the AppData folder you'll need to enable View Hidden Items in File Explorer.  

Those are all .log files. You must have view of file extensions disabled in File Explorer.  

No problems evident in any of those files - it installs, updates and runs without error apparently.

What if you set C:/users//AppData/Local/Programs/Paradox Interactive/launcher-v2.2021.2/paradox launcher.exe to run as the Windows Admin user, does it launch CK3 then?  

That's the error you get when you run paradox launcher.exe directly by double clicking on it. It is designed to only be run from Steam.

Right click on paradox launcher.exe , properties, compatibility, and tick the Run as Admin box in there. May as well do the same with dowser.exe (in the Steam CK3 folder) and bootstrapper-v2.exe . Then start the game from Steam.