I just started my bot @LesbianHexbearSupercharger@hexbear.net; and it's begun subscribing to a ridiculous amount of communities. This is important because in order for a federated community to appear in the all page one member of the local instance must subscribe to that community. Some new communities I can already see are /c/UnixPorn and /c/SelfHost. Posts might take a while to populate, though, as these are new communities Hexbear hasn't yet seen
Thanks to @Char@mander.xyz for the advice in this thread.
Please note, hornyposters, that I've disabled subscribing to NSFW communities.
Make an account there and search for it. Actually, you could just use their search bar without logging in.
I'm not wondering about a specific instance, I'm wondering if it's possible to know all the instances currently propagating each comm individually.