At the bottom right of every page, you can click on the “Instances” button (or just go to https://lemmy.zip/instances) to see what instances your site is federated with/is defederated from. lemmy.ml is under linked, so lemmy.zip is federating with them.

What you may be running into is that on this smaller instance, you may need to discover the communities:

These previous ways [searching for instances] will only show communities that are already known to the instance. Especially if you joined a small or inactive Lemmy instance, there will be few communities to discover. You can find more communities by browsing different Lemmy instances, or using the Lemmy Community Browser. When you found a community that you want to follow, enter its URL (e.g. https://feddit.de/c/main) or the identifier (e.g. !main@feddit.de) into the search field of your own Lemmy instance. Lemmy will then fetch the community from its original instance, and allow you to interact with it. The same method also works to fetch users, posts or comments from other instances.

(from the join-lemmy docs)