According to 9to5Mac , last year, Twitter added the option for users to sign in with a physical security key as a two-factor authentication method, but you must enable another authentication method to use it. Show Twitter are improving this feature to allow users to add key security without authentication methods enabled two other elements in your account.
Shared by the Twitter Support account, the security key can now be the only two-factor authentication option in both mobile apps and websites. With this new feature, users can simply set up a physical security key without having to add a text message or authentication code for backups.

Twitter explains this change is important because not every user may have or want a two-factor authentication method other than a security key, such as someone not wanting to send their phone number to their device. Twitter owner.For the uninitiated, a physical security key is a small device that stores authentication codes for apps and websites. This way, no one can log into your account without access to the physical key. Apple added support for physical security keys with iOS 13.3, which work through Lightning/USB-C connections or even NFC on compatible devices.According to Twitter, the new feature is now rolling out to users in the iOS and Android apps, as well as the Twitter website.