I imagine they are done with D&D. It's obvious they're not fans of the ruleset and I think that BG3 has earned them a lot of money, allowed them to expand,and established them as a leading studio. I imagine they'll either make DOS3 or something completely different. Either path will leave them in full control of the mechanics ruleset, lore etc.
BG3 was always more about leveraging D&D to strengthen the Larian brand.
“Why are you booing me, I’m right!”