On a side note, there are definitely hidden classes in the Baldurs Gate 3 like Fiend, Monstrosity and etc in the game, but so far we only can change legally into mind flayer via game and commands. All creatures in the game, player and NPC alike have own class, which means that player possibly can use the models, skins, animations and etc. since the game only recently came out it will take some time for modders to find the skins, but there are already mods that allow goblin creation in character creator.

Of course, needs to add that some of these skins are not compatible with combat animations, so probably that is why they are not available also. Imagine a cat holding a massive two handed sword. Hilarious.