Nostr is just Mastodon or IRC with automatic multiposting.

Users must selfhost data for decentralized socials to work. One big problem with running a Twitter-like social media, Twitter itself included, is that hosting UGC is just risk without rewards. Users don't pay for the bandwidth, advertisers don't like competing quality UGC(they're possibly even angry about social media that it keeps undermining their "creatives" investment), just no one pays for it.

So, a Mastodon alternative has to be selfhosted by default, and infinitely easy to set up for selfhost. "First, connect to your spare Pi with a global IPv4 address" is out of question. Multihop P2P likely won't work either.