We have Lemmy.world, Lemmy.ml, beehaw.org, I think even yiffit.net. If I log in using wefwef it asks me where I want to login. And when I make a new account using another instance, it says ”… Lemmy is federated, so you can interact with everything on lemmy.ml even if you’re registered on a different instance.“ So if I’m registered on lemmy.world, how can I interact with lemmy.ml?
I couldn’t see the community I made on lemmy.world in lemm.ee until I searched for it multiple times until it finally showed up. So some users may believe the community they’re searching for may not exist, even though it does on an another instance. Best to use Lemmy Explorer just in case when looking for a community.