For GoG, the process is similar, at least it was for me.
[1] Right click on BG3 in GoG, select Show Folder. Leave that open a bit.
[2] Start BG 3, Delete Campaigns.
[3] Uninstall from GoG. Check "Also remove my savegames and local data" when it pops up, UNLESS you want to save them for...some reason. Probably don't do this. Loss can be healthy for growth! If you do want to keep them, copy them from your local Larian folder (see below [4a]) to a safer location.
[4] Remove all Mods. Some from the folder in [1] and some from your local Larian folder. Mine was at:
[4a] C:\Users\<YOUR USER>\AppData\Local\Larian Studios.
[5] Make sure that folder you left open at [1] above is now empty, as is your local Larian folder from [4a].
Okay! This should now clear you for Baldur's Gate 3 on GoG!
Thanks for this, Sardaukar!!