I found this instance https://thefedi.forum/world (found here https://nodebb.fediverse.observer/list )
To follow a community, copy the ID of the Fediverse community, and on nodeBB click the magnifying glass on the right side to search and paste in the community ID in there (and delete the exclamation mark, like television@piefed.social)
change the dropdown to search “in categories” and it should show up like this https://thefedi.forum/search?in=categories&%3Bterm=television%40piefed.social
Open the community, click “Not Watching” to choose either “Watching” or “Tracking” and then new posts/comments will be synchronized in, and you should be able to join in on the discussions!


You seem more familiar with Mastodon than me:-).
Mostly this is just how the Threadiverse is designed to work. PieFed might do differently, but Lemmy has always been this way. That said, it is reportedly about to get worse/better (at the same time) as the choice as to what communities will show up for new instances will now fall under the centralized authority of Lemmy.ml directly - so e.g. anything defederated from it will no longer be considered part of the Threadiverse, at least by default (although that’s easy enough to override by adding the community manually). It is notable though that previously I believe zero communities were added by default, at least automatically (and yet when that update deploys and some do, it will only get more confusing to find out why some instances, decided by Lemmy.ml to not be worthy by their criteria, will not be part of that). It is also far more confusing than I let on here, and in ways that I do not fully know myself, since just because an instance is “aware” of a community does not mean that it is “subscribed” to it.
There is simply no way that the federated model is anything at all like “just using email”, as people claim. The defederations make it an entirely different thing where instead of having a fully connected graph we have only a partially connected one.
That all sounds pretty gloomy, on the whole.
If Lemmy.ml’s founders didn’t have such a controversial reputation, I’d be a lot more sanguine about all that…
It’s just one more step in a LONG line of many. Fortunately, PieFed exists:-).