It actually states that you may transfer your rights to the game to another person, which is, like... wow.
I'm not sure if I've ever seen this in another steam-connected game.
I still dislike the wording around the fact that the TOS can be changed at any time, and refusing revokes your right to playing it (without any compensation), but that's pretty much industry standard (unfortunately). This however, stood out to me.
P.S: If any of y'all have some extraordinary TOS's for other games that stand out in good (or bad) way feel free to share, it'd be interesting to know if there are others!
I wonder if there’s a way to transfer the game from my Steam account to my GOG account.
There is none in the way of a transfer. Neither Steam nor GOG will give you a copy of the game in exchange for another platform's copy, nor give you a copy on a competing platform in exchange for theirs.
This boils down to if your method of ownership supports it, you can do it. Neither Steam nor GOG support it. A physical disk copy would support it, for instance, so you'd be entirely allowed to transfer ownership of your physical disk copy of the game.
With GOG, you could theoretically download the offline installer, give that to someone else and then ask GOG support to remove BG3 from your account, and be fully abiding with the EULA conditions.
But that wouldn't give you a Steam copy, which is the scenario I was describing, along with the inverse mentioned in the original comment. There is no method supported by GOG or Steam to transfer a game to a competing platform.
Also in your case, the receiver would only have that one offline installer, the game wouldn't be in their GOG library, and they wouldn't get future updates.