Asklemmy

Suuuuper new to Lemmy, so apologies in advamce if this is a particularly stupid question. DDG has been no help.

I'm a member of midwest.social. I'd like to subscribe, and post to, a community (sub?) on another server. I know the other server is federated with midwest.social, because I can see other subs, and I know the sub on the foreign server (in this case, lemmy.ml), which I found with DDG.

So why can't I find the sub in Jerboa? I've searched by name, by name including server, by every combination of reference I can think of. !, #, @.

It's a technical sub, and I can't imagine it's been intentionally blocked. So I'm thinking that maybe Lemmy is whitelist-based? Do admins have to explicitly include subs from other instances? Or is there some magic that I've somehow missed about how to get to a federated sub that maybe nobody has yet accessed on the instance I've joined?

I found an old (1y) discussion about how to make Lemmy more accessible to new users. Someone offhand referenced this topic (accessing federated subs) needing more clarity, but with no explanation. A pointer to a how-to would be handy; maybe answers will help some future user when they find this post through whichever fad search engine privacy wonks are using in a couple of years.