In Sept 8th, the boss of Larian said that only a part of the studio still works on BG3, and the others are already working on another big project/game. We can expect they'll continue to work on BG3 until sept 2024 at least.
As a French, there's also some French game sites that read a lot of the Reddit & the Forum, thinking one of the next major Patches will be a major upgrade about Karlach based on datamining of the new game files (and the fact all the main asks from the players are all datamined... all except, probably, the most expected : Karlach) https://www.reddit.com/r/BaldursGate3/s/bXUDiULYzt.
About their new game, there's no information yet but they have all my trust if they want to release a BG4.
