On flutter it is possible to log in with your email/username and password. Then after checking his information, asked for the second authentication factor(example: totp/email/sms)

hey! Yes, it is possible - checkout the "how it works" and the "backend setup" section of this guide: https://supertokens.com/docs/mfa/introduction

on the documentation I saw that flutter was not supported

well.. we do have a flutter SDK that is a little outdated. Thats why