For the record I don't use Twitter or Reddit, and the only thing I use Discord for is playing Dungeons & Dragons, precisely because I know a lot of online communities are toxic (or quickly and easily become so) and want no part of that negativity.
As I see it a large part of the negativity (right now, at any rate) is that Endwalker didn't play out the way a lot of people here wanted it to - Hydaelyn / Venat was given a sympathetic portrayal, wonky time shenanigans were afoot, and the story veered more in a traditional fantasy direction than the political intrigue that seems to be more popular among this Forum's frequent users; so people have decided to go Cinema Sins on it and pick apart all the flaws, real or imagined, in how its story and characters played out. Shadowbringers received nothing but glowing praise.