In 2018 Twitter implemented support for hardware security keys. These are physical keys, small enough to fit on a keyring, to prevent certain types of accounts hacks. However, technical limitations meant that these accounts could only be accessed from a computer. Twitter has solved this issue by implementing WebAuthn protocol, this brings hardware security keys to more devices.
This means that users with security keys for their Twitter account can now login from mobile devices as long as they’re using a compatible key. Security keys are recommended for high profile account holders, such as journalists and politicians. Twitter even rolled them out to their own staff after a cyberattack which abused an ‘admin’ tool.