If you want to use a security key with your Apple account, you’ll need two keys
If you want to use a security key with your Apple account, you’ll need two keys – By Jay Peters The Verge
Apple just added support for security keys to secure your Apple ID with its latest iOS and macOS updates, but to actually set up your keys with your account, you’ll need to have at least two security keys on hand, according to an Apple support document (via MacRumors).