2 Factor Authentification

You are ill-informed. The system was supposed to work for everyone and in-general OTPs work this way only.

https://en.wikipedia.org/wiki/One-time_password

Everytime a user logs in, he is forced to enter the OTP. MyBB by default allows sessions that do not expire. Thus if you are logged in on PC-A, you will remain logged in unless you switch your browser, clear your cookies, etc. OTPs were implemented to make use of this feature, ensuring that user has to enter his OTP only when he logs in from a new device or browser.

2FA has no advantage over OTPs except that the passwords will arrive late if you have a slow mail server.