@Rikudou_Sage has the answer to see which instances are linked and blocked by any particular instance
defederating/blocking is not bilateral – instance A can block instance B without instance B blocking instance A
federating/linking is initiated when you search, browse, or subscribe to another community from your home instance – no need to send a request to your admin
even then, you still won’t see anything from instances your instance has blocked – which is why it is important to pick a home instance whose policies you agree with