I dunno how to hotlink, but if you scroll to the active users graph at fedidb.org/software/lemmy you can see there’s been like a 25% dropoff in active users since the peak in July. Lemmy has still grown 50x since May, and it’s much MUCH more active than it was then. But we’ve definitely crested a peak and not everyone who gave Lemmy a shot then is sticking around in a monthly basis.
This isn’t necessarily bad. Lemmy is still young and has many rough edges, it wasn’t realistic to win all the users that tried it on ease-of-use in a head to head with reddit. And Mastodon has had multiple growth waves interspersed with periods of declining usage, but with the spikes has grown ie remained stable overall. Early-stage commercial social media have big ups and downs in engagement and growth as well, and just like lemmy those ups and downs are often externally driven… when competitors mess up, when a big global news story hits, when a major sporting event happens… these can all be catalysts for one-time growth. It’s not a straight line.
Time will tell what user level we stabilize at in the short-term and what events spur new growth, but it’s normal to have a big expansion be followed by some degree of contraction.