I noticed that some communities on lemmy.ml are unable to be seen on other instances. For instance, federating the lemmy community works fine:

https://sh.itjust.works/c/lemmy@lemmy.ml

But federating the kubuntu community returns 404: couldnt_find_community:

https://sh.itjust.works/c/kubuntu@lemmy.ml

I'm certain that second one should work... I've found perhaps two dozen other communities that have the same problem. Meanwhile, dozens of others work fine.

Edit: @aspseka@sh.itjust.works suggested I try searching for the community first. I had actually tried this but it didn't work, which is why I started trying the deep link approach above; that worked for some communities.

Turns out the deep link by itself will not discover new communities, only searching for them will, and the search can take a long time and will show "No results" for a little while.

So if you're experiencing this, search instead for [!community_name@instance.host](/c/community_name@instance.host) from the remote instance, then the deep link will start working.