@nyan couple of hours of research in and I’m baffled. There is no apparent mechanism for discovery in ActivityPub.
It appears as if the protocol has simply ignored the literal first step of all social interaction: Observation.
Take lemmy as an example, if I visit beehaw.org directly I can click on “Communities” and get a list of them. Yet, there is no way I could identify to get this via ActivityPub. I’m completely and utterly baffled.

@nyan @leopardboy that. Although even accessing federated content on demand would work. There’s no technical reason to limit what you display to the user to one instance. If I want to access lemmy.cafe from mastodon.social why is that not possible? It’s federated, so I should be able to do that. The API definitely allows it, as seen in this thread. The User Interface just doesn’t deal with it. I understand the limitations at play quite well, which is why I’m thinking dedicated client.

@leopardboy not as such. I just want a way to access the entire fediverse from one tool, warts and all. I assume such a thing doesn’t exist. Yet. A state I will probably begin working on momentarily.

@leopardboy I’m coming from the PoV of accessing it. Every fediverse compatible instance is just another store of messages. Technically I have part of this, I’m writing this very reply on mastodon.social, but I can’t explore beehaw.org unless I leave mastodon.social and go there. Basically it would mean treating the instance you work from as just an email account while showing compatible content from any source and allowing you to interact with it as is.