Dear Palaiologou Vlasis,
Good day! Thank you for posting to Microsoft Community. We are happy to assist you.
Based on your description, you want to know the difference between enabling and enforcing MFA.
Enabling MFA for a user means that the user has the option to set up MFA, but it is not required. Enforcing MFA means that the user is required to set up MFA and cannot access their account until they have completed the MFA setup process.
If you enforce MFA for a user, they will be prompted to set up MFA the next time they log in to their account. They will not be able to access their account until they have completed the MFA setup process. Once they have completed the setup process, they will be required to use MFA every time they log in to their account.
Enabling MFA gives the user the option to set it up, but they can still access their account without MFA. Enforcing MFA requires the user to set it up and use it every time they log in.
I hope the information abave can be usesful. If there is any update or I misunderstand you, please feel free to let me know. I will continue to assist you. Your understanding and co-operation are highly appreciated.
Thanks for your precious time. Have a nice day.
Sincerely,
Sherry | Microsoft Community Moderator