The last time I "joined" a fandom (as in like, I cared about discourse, drama, and actively sought out people to talk to about the piece of media) was Undertale, everything else has just kinda been grandfathered in though I actively ignore anything to do with fandom happenings. Looking back, I think it laid the groundwork for a lot of things that we see happening nowadays. There was a weird purity culture to it, like not just disliking or not caring for nsfw art, but active hatred and aggression towards artists that drew it. And it was somehow this big affront to the character and everyone who had to see the art if you drew anything beyond PG-13.
Maybe this one was just my view, but there were also a lot more otherkin than I'd ever seen before, and nowadays that shits rampant. Kinners were Very Normal about fanart of their believed other, of course, why wouldn't they be?
All of the memes and in-jokes sucked, but I think that's actually just every fandom (or I'm just no fun).
The truly enlightened view is accepting that any gathering of people on the internet where the only shared thing is a piece of media will overwhelmingly attract a majority of psychopaths and weirdos who have nothing but the clout they believe themselves to have online.