What's the difference between Heroku MFA and Heroku 2FA?
Heroku 2FA is a deprecated feature that allowed users to use an authenticator app as a second factor.
Heroku MFA or Multi-factor Authentication allows you to use a broader variety of authentication factors for better security and convenience. See Heroku Multi-factor Authentication for a list of authentication methods.
If you previously enabled Heroku 2FA, your authenticator app, SMS and backup codes continue to work with MFA.
Note that Heroku discontinued the use of SMS for multi-factor authentication in June, 2022.