Monero

do not understand what nostr does that mastodon does not

It has a really nice ethos for the coding side of it and is very easy to make stuff for. The only mandatory thing to implement is extremely short, and all of the documentation is in a single github that takes contributions from basically anyone for additions. It can very plausibly be used for stuff that isn't like Twitter. Having cryptographic keys instead of accounts is a good concept, so are relays, makes it so there isn't any given server that has a lot of power over you as a user. If you're not a developer and don't care about that stuff then yeah it doesn't really have much mastodon doesn't right now but it's still cool imo.

OK...

Nostr is a (mostly) use case agnostic transport protocol. It consists of relays, which only relay messages, and user clients, which only sign messages and send them to relays. Clients can send to as many relays as they like, ensuring censorship resistance, and users don't have usernames and accounts and all that, only keypairs.

Now, lots of people have built on top of it ways to "verify" with servers, the maintainer has built into the protocol special types of messages that are things like account descriptions and avatars, and most of the development is focused on microblogging. But that's not all it can do.

It's as pointless as monero is in the face of bitcoin: it isn't pointless. It's a very good idea actually. I think the protocol has become too convoluted, but it does what we need it to do. It is censorship resistant, potentially anonymous publishing on the clearnet.

The video covers why Nostr is better than Mastedon. Mastedon makes you reliant on a federated admin who can ban you. And federation relies upon DNS and IP addresses for identity, as opposed to encryption as identity.