Well, there are two issues with BG3 and DD5 rules :

1 - First, the Larian additions that breaks DD5 rules. This is discussed in many threads : high ground, surfaces, backstab, jump, lack of some combat actions present in the PhB, etc ...
2 - Second, and it is not negligible : a very poor User Interface that is not convenient at all. Games as Solasta or before Pathfinder KM (for Pathfinder rules that are even more complex than DD5), POE, etc ... did a huge work to define a convenient (and most of the time nice / immersive) User Interface that helps the player to interact with the system.

For me, Larian should work on these two aspects. Despite the disappointment of some DD / BG players who may be disappointed by the fact BG3 is too far from DD rules, also that will show that Larian has difficulties to do something else than DOS games whereas this BG3 game should be an opportunity to show that Larian can do different games.