Mods work perfectly fine with the GOG release, as TheMrHuggles states
Quite simply what you're saying isn't correct, No such thing as Steam mods, or GOG mods
They are identical, and usually work for every game, irrespective of the store client used.
Individual game updates, specific to one site, can cause issues, but it's not because of the site, it's because of the game version used.
With W3 that was the GOG GOTY edition, which is a different version to Steam's.
A very mall difference caused by integrating the DLC in one package.
it affected the few mods using the Main Menu, and that issue was fixed by this mod. UPatch - Unification Patch by Wasteland Ghost=2134
Mods that check for installed DLC, need the correct script merger edits, to stop the removed DLC check being reapplied.
Even SW (Steam Workshop) mods are no different than NM (NexusMods) versions, except in the folder location they go in.
SW forces mods into it's own folder system, whilst NM (and GOG), use the games normal folder structure for mods.
I've never use SW, as it forces auto game, and mod updates, which can, and often will will break your other mods.
It's never stopped me downloading (Subscribing), just long enough to get a specific mod.
Make it into an archive, with a corrected folder structure.
Then you must Immediately delete the SW mod, and unsubscribe, to stop Steam downloading it again.
Biggest issue with SW is you must own the game on Steam to download the mods.
That's all kinds of fucked up, as mods should be freely available to all owners.
No games should support SW because of this, unless they never get sold on another store client., or on GOG.
There is absolutely no such thing as a "Steam Mod", or a "GOG Mod".
Only mods for different versions of the game. Not the damn store client.
You, Sir, are THE MAN! Thank you for that informative, specific, and helpful post! Seriously, I have been reading through such TRASH for the last hour+ trying to verify what you've said regarding the differences in how Mods work for The Witcher 3 GOTY GOG Edition....and the sheer amount of BULL**IT I've read is staggering. Thank you for clearing this up, and, I could not agree more with what you said regarding the Steam Workshop. One of the pillars of PC Gaming is Free Modding for PC Games, and I detest anything that actively tries to chip away at the way Mods have always been handled for PC Games. Anyways, I'd better get off the soap box before I get too invested lol, thank you again for your post!
EDIT: Oh and I know I might sound a bit too excited about all of this, but I was really getting blown away by all of the Fanboy nonsense just trying to verify Mod information (really, do so many Witcher fanboys have to slam Elder Scrolls games just to prove their love for the Witcher? We're not allowed to enjoy both without being flamed? Come on, guys, leave that for the Console-Only crowd, PC Gamers used to be above this, didn't they??). That said, I was literally cheering when I saw a post that skipped through all of that and got into the HOW and WHY promptly.Thanks again UhuruNUru.