.. I restored my backup by deleting the .paradoxinteractive directory again...
Dislcaimer : I'm just another forum (and Windows) user.
May i ask why you restored a backup ?
All you need and can keep is the "mod" and "save games" folders.
I would advise against keeping any other older files.
..and add the obligatory (reltively, see above) clean install recommendation.
Now more of my potentially as helpful, as useless 2cents :
Regarding Nvidia i read a few had issues with older NVidia drivers.
Another issue came up when Geforce Experience had fullscreen set for the game when
it was set to Borderless in settings.txt. No idea if this is relevant on Linux.
Not much else to add, than to see if the dlc folder is in lowercase.
I recall someone stating that his Linux game didn't even start with it as uppercase DLC.
A little weird as i otherwise only recall issues with the DLC tab, but i don't know.
Just another shot in the dark.