On the fediverse it currently is eternal September.
I was there before the reddit explosion when the majority of the posts on the fediverse were from one guy who just vomited cccp propaganda all day. I think it's in a much more interesting place right now.
Reddit otoh started to become boomer-Facebook-meme-town some time around the onset of COVID and then hockey sticked last year.
I actually dislike the fedi fragmentation too much. Yes, ik that's the appeal for some people but I really don't like just how split it is