Backup codes are one-time recovery codes for a sign-in where your normal passkey, authenticator app, mobile approval, or email code is unavailable.
Open Settings → Security → Backup codes and select Manage. Generate the codes, save them outside LightDrive, and keep them where another person cannot read them.
Each code works once. Mark a used code or remove it from your saved copy. Generating a new set invalidates the previous set, so replace every stored copy.
Backup codes do not replace the account password and should not be used as an everyday sign-in method.