As mentioned, the Passkeys are synced in iCloud, so a lost device doesn't mean the credentials are lost.

If you still can log in to iCloud, you're fine.

If your Apple ID password has been changed, Apple provides a workflow to regain access to your Apple ID [1].

There's also a process for account recovery for situations where you can't access your Apple ID because of two-factor authentication [2].

[1] https://iforgot.apple.com [2] https://support.apple.com/en-us/HT204921