The Apple ID recovery key is a feature that allows you to add additional security to your account. At one point (I couldn’t determine when), Apple removed it from its operating systems. But with iOS 14, the option is again present.
Apple ID recovery key
When you create a recovery key, the only way to reset your password is to use another device already signed in with your Apple ID or to enter your recovery key. It’s an extra layer of security, but it means that if you lose your key, you can be permanently locked your Apple ID. Proceed with caution.
Again, make sure you have a copy or two of your recovery key. In 2014, Owen Williams of TheNextWeb had a close call when he almost lost his key. In this situation, Apple Support can do very little for you, if it can even do anything.