Perhaps you could explain?
Decentralized means there is no center
I would add that Distributed to me seems there are no inherent “domains” you need to belong to, like for example email is federated but with scuttlebutt you’re identified by your public key and a hub is just a dumb relay and you can have many.
Non-federated routing alternatives include Kademlia (used in BitTorrent) and simple flooding/gossipping (like in Kazaa) or ad-hoc networks
For that matter, what is the authority at the top of email? You and I can set up an email server and start talking to each other right now without anyone's permission. We don't have to be connected to anyone else, and we don't have any authority that can control our implementations or even that keeps track of what servers exist.
I don't get the comparison between Email or Mastadon to ICANN.