[ezfe]

At least on iOS, passkeys are stored locally in Keychain, even if they're also synced over iCloud (when enabled).

[makeitdouble]

I'd assume it's the same story on iOS, as you won't get access to Keychain if your Apple ID is locked ?

Provided Apple has fewer services and less surface for your account to get banned, but that's still a valid concern.

[zie]

In my experience on iOS, you can't make Passkeys work without also turning on syncing, that's sort of the entire point of Passkeys, otherwise they would just be WebAuthN tokens.