@nikitonsky I assumed by passkeys you meant something like Yubikey or Nitrokey. Once a key is written there, it can't be extracted by "normal" means. If you want a backup, you buy two devices and write your keys to both of them¹
[1] https://support.yubico.com/hc/en-us/articles/360016614880-Can-I-duplicate-a-YubiKey
@bemyak no, this one https://en.wikipedia.org/wiki/Passkey