Nostr is a weird being. You are correct that it is not peer-to-peer like Monero is. However, it’s not quite federated in the same way that ActivityPub is.
When using Nostr clients, you actually publish your same data to like six different relays at the same time. It has the built-in assumption that some of those relays are going to be down at any given time and so by publishing to like six at once you get data redundancy.
Nostr is a weird being. You are correct that it is not peer-to-peer like Monero is. However, it’s not quite federated in the same way that ActivityPub is.
When using Nostr clients, you actually publish your same data to like six different relays at the same time. It has the built-in assumption that some of those relays are going to be down at any given time and so by publishing to like six at once you get data redundancy.