In one of my threads, I think it was the suggestion thread, I said for people who don't play DnD (probably a large group of individuals) to make a small animated cutscene (a la DoS cutscenes, animated but not too extensive) explaining the Avernus campaign, briefly. I don't play DnD and watched an hour video on Youtube that explained the entire campaign. It was a bit of a slog, but at least I get where this is coming from.
To start the game 100 years after the last one is fine, but there needs to a be a bridge for the people that don't play the tabletop included at the start so you can connect a bit better.
If anything, this thread shows that many players who've been through the first act still don't know what's up with the Tieflings. Or Decent Into Avernus. A graphical style intro narrative (like what you might see in Dragon Age with moving pictures) could serve this well. No need for a full-on CG movie.