The Battle of Betazed was one of the most important incidents in the Dominion War and Star Trek: Lower Decks finally explains why it was such a vital target for the Changelings.
I really hope that they don't try to Cinematic Universe this; it should be possible to watch and enjoy a Star Trek movie without having seen any other recent Star Trek movies or TV shows, and you shouldn't have to go to all of the movies to understand what's going on in any specific one.
(a trilogy is fine - that's what 2/3/4 were - but keep the story arc to that size or smaller; of course 2 was also a continuation of a specific Original Series episode, but you didn't actually need to have seen it to understand immediately what was going on with everyone)