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?
You can use Lemmy Explorer to explore. Type your home instance in the top by tapping the home and it will create all the proper links for tapping and getting to other instances.
Essentially a link like !asklemmy@lemmy.ml will get you there from any instance. The first part being the community and the second being the instance.
These also should lead to the same community. https://lemmy.world/c/asklemmy@lemmy.ml https://lemmy.ml/c/asklemmy
Also if you sort by all on an instance that’s populated well you should see most of the fediverse as it is already and can just search within it for what you’re looking for.