I think I might have found an answer. Some communities might not be federated yet on that instance. So you might have to search the whole "[email protected]" and get no results. Then a few minutes later search for just "community" and it should be there.
I have previously tried just "windows_help" as well and it wasn't there yet. Definitely makes this confusing.
You don't need to use desktop mode for old Reddit. It just makes things smaller but doesn't seem to change anything.