Well if i recall right there was a interview with Sven in 2019 fextralife, where he was asked on what ruleset BG3 will be based upon... and Sven dirctly stated it will be based on Dnd5e, or well, as much as possible, as its still a video game and some things wont work...
i can probably dig it up... but thats one of the many that comes to mind...
actually found it
https://fextralife.com/baldurs-gate-3-interview-with-larian-and-wizards-of-the-coast/its second question, its a straight ask, what rule set will you use... we ported all of 5e and will bla bla---
