GOO have nothing to do with Illithids tho.
Are you talking about in the game generally, or something you have learned about BG3? Because in my experience of 40 years playing D&D elder brains, aboleth, and generally any powerful aberration are considered suitable GOO warlock patrons.
So, unless there is evidence of Cthulhu or Tharizdun uncovered in datamining, I think the tadpole (as a conduit) is the most likely GOO patron.
