I have been using Lemmy for 20 days, at first I opened an account at Lemmy.world because you can join without writing a text and waiting approval. I have been enjoying the experience overall but despite the admin teans best efforts Lemmy.world has been experiencing some serious performance issues. If you want to avoid that join a smaller instance, preferably hosted in your country. I joined discuss.tchncs.de today and everything is so much faster it has added benefit of being able to see beehaw.org posts too. It will improve not only your but all other Lemmy.world users experience too.
From what I understand about Lemmy, the only way to disable signups completely is by defederating. Meaning, you would not be able to view other communities from other Lemmy instances like .world or beehaw.
To get around this, you can switch to application signup like beehaw and just ignore/reject every application but this would also mean that anyone can view your instance as a guest. Like you can go to lemmy.world and view posts and comments without logging in
Atleast, that’s what I understand. Maybe someone can correct me if I’m wrong.
You can’t disable registrations from what I’m understanding but you can make them pending some approval. So in my case I’d just ignore any registration done.