This site is currently struggling to handle the amount of new users. I have already upgraded the server, but it will go down regardless if half of Reddit tries to join.
However Lemmy is federated software, meaning you can interact seamlessly with communities on other instances like beehaw.org or lemmy.one. The documentation explains in more detail how this works. Use the instance list to find one where you can register. Then use the Community Browser to find interesting communities. Paste the community url into the search field to follow it.
You can help other Reddit refugees by inviting them to the same Lemmy instance where you joined. This way we can spread the load across many different servers. And users with similar interests will end up together on the same instances. Others on the same instance can also automatically see posts from all the communities that you follow.
Edit: If you moderate a large subreddit, do not link your users directly to lemmy.ml in your announcements. That way the server will only go down sooner.
Not sure why you reference Matrix, which has even worse scaling issues as it indeed tries to replicate nearly the entire network on every server.
The Fediverse is really just working how the general web does, just with some standardized API for websites to interact. It’s not perfect, but it works and has proven to be relatively scalable.
It sounds a bit like you had a bit too much of the Bluesky cool-aid, which indeed replicates nearly all of the mistakes of Matrix and makes it impossible to scale via small community owned servers instead of big company owned data-centers (which might be by design?).