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.
We need a way to search across servers for a community
Try this: https://browse.feddit.de/
I’ll agree that fetching a new community is much more awkward than it should be.
You can do that as soon as your instance knows about that community.