these are a few information that I copied from Fandom page that I think that possibly relates to what's going on in BG3.
For others deities (like Shar) the Second Sundering resulted in a loss of power and influence. The Lady of Loss suffered greatly in the wake of the defeat of the Shadovar and the destruction of the city of Shade in the battle with the forces of Myth Drannor. Telamont Tanthul and most of the Princes of Shade were also killed, further weakening the goddess of darkness (probably the reason why we see so many Sharrans' work/influence in the game).
Mystra was still able to directly commune with her remaining Chosen. (how Gale got hooked up with Mystra).
The Dead Three, greatly reduced in power, decided to remain on Toril, living as quasi-divine mortals, to spread the word of their return, gather more worshipers, and influence events in their favour.
