Number of (active) Lemmy users seems to stabilize and I think this is a great thing. Indeed we got a lot of users when reddit shutdown its API (I was among them despite being a long time oss user), many have left, but the community seems now to stabilize to ~ ½ of the big grow in june '23. I think this is very nice for lemmy, we can be proud of this project.
The stats come from: https://fedidb.org/software/lemmy
There was a huge surge of people on reddit creating accounts driven by the API saga, it wasn't natural growth. The normal expectation is that most people would only stick around a short time. Having 50% remaining after the peak is honestly impressive! I'd expect it to continue falling for a while but eventually it should start to rise when natural growth exceeds the attrition from that event.