I’ve seen this mentioned a few times already: people wondering why certain communities don’t show up in their instance. You need to first search for that community via the magnifying glass icon and type in “!communityname@instance.domain”
Notice the exclamation mark at the beginning. Might take a few seconds. This will teach your instance about the remote community.
Removed by mod
Actually that’s a great idea! I should add that info to the sidebar of mine.
It already is, open your community in incognito mode. It just doesn’t show because you’re already subscribed.