Confirmed are Chris Pine, Rege-Jean Page, Hugh Grant, Jason Wong, Daisy Head, Justice Smith, Michelle Rodriguez. Hugh Grant, and Sophia Lillis. Dave Arneson has a writer's credit, with the screenplay by two guys I don't know (but one did Spider-Man: Homecoming, so there's that.)
New rumor today is that Benedict Cumberbatch has been cast.
There have been a lot of rumors over the years about the content, but nothing has been confirmed. At one point it was supposed to be a Drizzt movie (although the makeup could be problematic in this day and age, and D&D is being very careful with the Drow right now anyway.)
All that is known for sure is this set photo: