Do you actually have no audio at all? I can still hear the background noises in the menu, but otherwise I'm having the same issue... No dialog in the intro movie, nor in the character intros... Just the background ambient noises.
I've tried all the same things as you. DirectX, Vulcan, driver verification, spatial audio, restarted, verified files, checked that game was going to correct audio device, running bg3 directly...
Nothing changes anything.