recovery key option

If you are using two-step verification you were given a recovery key when you set it up (and told not to lose it).

If you lost your Recovery Key

As long as you remember your Apple ID password and still have access to one of your trusted devices, you can sign in and create a new Recovery Key.

1. 1. Go to your Apple ID account page.
   2. Sign in with your password and trusted device.
   3. In the Security section, click Edit > Replace Lost Key.

Keep your new Recovery Key in a safe place. Your old Recovery Key won't work anymore and you can't use it to reset your password or access your account.

https://support.apple.com/HT202649

If you are using two-factor authentication:

If you previously enabled two-step verification with a recovery key on your account and you sign in on a device running iOS 11 or macOS High Sierra, your Apple ID is automatically updated to two-factor authentication. After your account is updated, you have the option to generate a new recovery key. This option is only available if you are updating an account from two-step verification to two-factor authentication. Learn how to create a recovery key.

https://developer.apple.com/support/authentication/

(My emphasis.) So if you have two-factor authentication and have never used two-step verification there is no recovery key.

Those steps are available here:

https://support.apple.com/en-us/HT202649

iOS does not, nor has it ever used recovery keys. FileVault on a Mac has a recovery key, as does your Apple ID if you use two step verification.