OSXDaily:

Resetting your Apple ID password is normally a pretty easy task, but if you don’t have access to the device that you’re already signed into, things could get super complicated and inconvenient. However, Apple offers another option with an Apple ID recovery key, which can be used to reset an Apple ID account as well.

Apple ID Recovery Key acts as an extra layer of security for your Apple account, in case you forget your password and lose access to your trusted device.

For your iPhone or iPad, you’ll need to be running iOS/iPadOS 14 or later, a pretty reasonable requirement.

Once you’ve created your recovery key:

From now on, you’ll have just two ways to reset the password for your Apple account. You can either reset the password from a device that you’re already logged into, or you can use the recovery key instead. The latter would prove to be a lifesaver when don’t have access to your trusted devices.

Interestingly, the Recovery Key is an old mechanism, removed a while back and then returning in iOS 14, et al.