Ah yeah, beyond the un-extractable private key thing and the wide support, there's nothing really special about passkeys. For cross-device stuff, IMO decentralised TEE cloud is the way to go, over FROST bunkers. Much much better UX. It's like nitro enclaves but decentralised. We use

dstack - Open Source Confidential Computing | Phala

Deploy secure applications with hardware-guaranteed privacy using TEE technology. Built for confidential AI, private cloud compute, and secure data...

for some related things and it's good. The problem there is that many people here will get upset that it uses a blockchain that's not Bitcoin. Even though you need a blockchain to orchestrate the TEEs, and Bitcoin doesn't have the functionality, and nostr clients would only ever interact with the TEEs and not the chain, etc etc.

@arthurfranca has some ideas of how to use passkeys in a smooth cross-app syncing flow. I don't know all the details and I'm not 100% sure it works, but it may work pretty well for some users.

Yes, I'm gonna use passkeys to help simplify nostr key management when accessing nostr apps. The nsecs will be importable/exportable. All the pieces are almost in place to put it online for everyone to test. I just need to go back to drinking coffee or someone to whip my back. Passkeys have become better with time. We don't need Apple/Google/MS/some-linux-distro-support anymore. E.g. Bitwarden (can be self-hosted) has a browser extension and native apps, supports passkeys and syncs keys across devices no matter the OS.