It is opt-in by user or by server: https://tags.pub/#connect
People can opt out even if their server is opted in:
https://tags.pub/#optout
We used to also connect people if they used open-registration relays, but I just turned that off, because people were surprised they were getting boosted:
https://socialwebfoundation.org/2026/06/28/unsubscribing-tags-pub-from-open-registration-relays/
