I just thought up a horror scenario.
Will a player with the game on GOG and a mod from Nexus be able to join my steam game with the exact same mod from the workshop?
Please let the answer be yes!
Or will the game be a "different version" and therefor be uncompatable?
The answer is basically YES.
GOG may take a little time (Usually in Hours, not days) to make the offline installers, once Galaxy gets the update, but other than that same game versions are the norm.
As far as mods go, it should make no difference, they are the same mod, just located in different folders.
No sure how Steam does it, with DOS but every Steam Workshop game I've used, has a Steam GameID number as a folder, and a ModID Number as the mod folder.
..\Steam\SteamApps\Workshop\Content\{GameID Number}\{ModID Number)\Assuming the normal Workshop setup, this is
Clean Hotbars mod
..\Steam\SteamApps\Workshop\Content\435150\1135790676\GOG
Assuming it's not changed from the Alpha, the Steam mods would go in your user documents folder, that's it.
..\Documents\Larian Studios\Divinity Original Sin 2\Mods\That's it for Steam mods.
The other location used, for mods not packaged for Steam is in the games folder.
..\Divinity - Original Sin II (GOG)\Data\Public\A Mods folder also existed for DOS EE, if that still works
..\Divinity - Original Sin II (GOG)\Data\Mods\Plus you can always overwrite the files directly, as with any game
..\Divinity - Original Sin II (GOG)\Data\Game runs in memory, not on drivesThe essential part though is as long as the mods contents are the same in both games, and used in both games, it won't make any difference where the folders are, as the games running in memory.
Same content running = same game, whether on Steam or not.