[fiddlerwoaroof]

This isn’t true as far as I can tell: when you create a passkey on iOS, the first screen prompts for which app to use to create the passkey and LastPass, at least, implements the necessary APIs

[cyberax]

Most users will not have them installed. And once you start using iCloud for them, migrating passkeys out of it is impossible.

You can't just install 1Password later and click "Import Passkeys".

[fiddlerwoaroof]

Maybe not, but you can install 1Password later, go to the account with the iCloud passkey and use it once, then use 1Password to generate a new passkey for that account. This flow is also generally better than trying to port keys between accounts, which adds a lot of security concerns.

[cyberax]

Once you have hundreds of accounts? Yeah, sure.