That's a different problem, and won't be solved by any P2P-platform. There are more than enough ways for discovering selfhosted content, people just don't use it.
… which means it’s a problem.
There are lots of options for running your own Mastodon/ ActivityPub implementation, etc—it’s not easy, though. This is purely a technical problem.
Of course, I am not really talking about Chirp clones here, but this is a pretty good analogue for comparison.