It should appear in the search of true instance, try again and wait a little bit for it to load if you're the first one from your instance instance to subscribe to that community.
If that doesn't work try searching the full url: lemmy.ml/c/todayilearned and it should come up.
Does this link work for you?
https://social.fossware.space/c/[email protected]
It's showing posts so I think it's already federated.