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.
Sadly, I feel like the Fediverse, based on ActivityPub, was fundamentally designed wrong for scaling potential. I do like Fedi and I like ActivityPub, but I think instances should not have to be responsible for all of this:
Because servers "own" the user accounts and communities it's not trivial for users to switch to a different instance, and as instances scale their costs go up slightly exponentially.
I wish the Fediverse from the beginning was a truly distributed content replication platform, usenet-style or Matrix-style, and every instance would add additional capacity to the network instead of hosting specific communities or users.
I guess it's a bit too late for a redesign now... Perhaps decentralized identifiers will take us there in some form in the future.
While it might not be too late for that update, it would require some reconciliation to happen. There's the potential for multiple users and communities of the same name across servers that would need to be considered.