So I managed to figure out how to download mod paks from the steam workshop for the Definitive Edition, and carefully chose only ones that were for Game Master Mode and had been updated since the version that I am running (3.6.117.3735) but am not sure how to use them. I first tried putting them in
D:\Gog Games\Divinity - Original Sin 2\DefEd\Data\Mods
but the game didn't seem to see them. But because I accidentally dropped one of them in:
D:\Gog Games\Divinity - Original Sin 2\DefEd\Data
I noticed that the .pak file did show up in the mods add ons list. So I moved all the mod paks there, and I can see them all, I see a description for them, I can give them a check mark and apply them but they don't seem to do anything. When I go into GM mode, I don't see any new levels or maps available to me. Now I do see the note that "Only Divinity 2 - Original Sins Definitive Edition add-ons are supported", so maybe these items are still in the wrong place.

Do I need to move these packs somewhere else? I'm not sure what the distinction between "adventures" and "add-ons" is and don't know whre to put "adventures". Or is there some way of accessing mods in GM mode that's not obvious to me? Any help would be greatly appreciated. Thanks.