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
Do the instances not interact with each other? Is it like playing a game in a different server and youll never see your friends in the game? Idk how it works
No, that's not how it works. Instances absolutely interact, that's the whole idea of federation. It can get more complicated than that if you want to get into the details of how it works, but that knowledge isn't in any way necessary to just use the platform.
So all lemmy servers can communicate with eachother, unless a server decided to "defederate" with another which cuts the connection.
Futhermore, mastodon and other fediverse projects can also communicate with lemmy and back, but since the format of the posts and comments is a bit different this might take some work for the devs to get working completely correctly.
They are (mostly) federated, which means that users from one can see what's on the others. There are a few exceptions to this, primarily for extremist content which are not federated with most of the other servers.
All four of the replies to your comment (as of now) are from users on different instances.
While the other replies are not incorrect, what they describe is users on Reddit posting on different subreddits.
What I am talking about are lots of niche subreddits (many even about the same topic!) thus that out of the few people that are here, there is simply no content, let alone discussions of the present content.