Wasn't i supposed to be able to use _any_ mastodon logon to _any_ mastodon server/instance?
I found this, which explains #federation pretty well: https://mastodon.help/#HowFederationWorksTheory tl;dr a new instance has no federation, and the federated feed will be empty, but as users follow, boost and interact with users on /other/ instances, federated links are built up automatically. Admins can subsequently block those federated links if they want. This is why I keep seeing posts from admins of new instances asking for boosts: it builds federations to their instance