[2022] Database migration failure / a decently sized list of attempts to fix it

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

Jammy_Jam said: I put the paradox_launcher_v2 path into my antivirus' exception list,

You need to put the .exe file in the exceptions list, including its whole path. Assuming you are on the current launcher that would be C:/users//AppData/Local/Programs/Paradox Interactive/launcher-v2.2022.1/paradox launcher.exe

You use Avast or AVG I assume?