i was just thinking this too… easy enough to see who we have defederated but idk bout the inverse … following !

This is actually surprisingly hard to do! People will get around to it I’m sure.

So far my most successful method is to googlefu my way through with keywords and browsing posts.

But, here’s some fun resources that can kinda-sorta-not-really help:

1. lemmy.fediverse.observer/list
2. lemmymap.feddit.de

The map in particular is extraordinarily cool but rather difficult to discern useful info from. I can tell you from it that lemmy.world is currently defederated with only one other Instance. Which is easy to figure out from there at this point.

You could manually look it up, again not the best answer to your question. https://fba.ryona.agency/

This doesn’t quite answer your question but has some info on defederation - https://lemmy.world/post/149743

For any given instance who decides what other instances to federate with? Is it just the arbitrary decision of the server maintainer? The mods? Democracy of the users?

If you put /instances after the URL, e.g. beehaw.org/instances, it will list all linked and blocked servers.

Lemmy the software publishes all (de)federations of an instance at the /instances endpoint

For example, Beehaw’s (de)federations are at https://beehaw.org/instances
and my own single-user instance has them at https://lemmy.w.on-t.work/instances (which is slightly different as I run Lemmy 0.18)

If you are looking for the reverse of this, there is a tool that shows that information, but the creators of it are suspicious to say the least (as in, will openly associate with KF kinda suspicious)