Looks like you are trying to access the account which is redirecting you to another tenant.
And there is a policy which needs you to go through MFA for you to access Azure portal.
You can try to login with url https://portal.azure.com/<your domain name>
This will directly redirect you to the directory that you are looking for.
If this still doesn't work, then you will have to get in touch with Global admin of the directory to understand why is the MFA getting prompted. If this is prompted due to conditional access policy then you can exclude your account from it.
Let me know if you have any further questions.
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