I bought CK II from Steam years ago. But oh no! Every time the game starts, it deletes the mod files!
With help of Paradox support we tried EVERYTHING, but nothing helped. I wated for years a fix, or someone having the same problem.
Recently I found out why. The game REQUIRES Steam Cloud enabled to play mods.
Alright, I don't want to use cloud service, I never have.
I see GoG has a cloud service too, but configuring it is disabled in GoG Galaxy.
Do mods word with GoG version of the game? Without cloud save?

ever figure it out?

the mod that adds a lot of events :
https://github.com/cybrxkhan/VIET-Events-Reborn/releases/latest

works for me on the gog version (i'm using offline installers, not galaxy)

to install :
on the page linked up there, under Asset, click on " Source Code (zip) "
this will download a " VIET-Events-Reborn-2.0.15.zip "

Once downloaded, open this archive with your favored archive manager (winzip, winrar, 7zip, the window built-in tool, whatever)

Now in this archive the 2 important things are the folder named "VIET Events" and the file named "VIET Events.mod"

Take them and move them to

C:\Users\YourUserName\Documents\Paradox Interactive\Crusader Kings II\mod\
( YourUserName being of course your user name on your computer)

or just click on your User Profile folder that is always on the desktop (at least on window 10) , then go to
...Documents\Paradox Interactive\Crusader Kings II\mod\

note : if there's not already a folder named "mod" in ...Documents\Paradox Interactive\Crusader Kings II\
just create one manually and name it exactly mod .

Once done that's all, you can then enable "VIET Events Reborn - A Flavor Event Mod" in the CK2 game launcher -> Mods tab