A cloud-based identity and access management service for securing user authentication and resource access
I would highly recommend that rather than setting the MFA per user, you create a Conditional Access policy (or enable the security defaults if you can)
https://learn.microsoft.com/en-us/azure/active-directory/authentication/howto-mfa-userstates
https://learn.microsoft.com/en-us/azure/active-directory/conditional-access/howto-conditional-access-policy-all-users-mfa
https://learn.microsoft.com/en-us/azure/active-directory/authentication/tutorial-enable-azure-mfa
But for your specific question:
Enforced The user is enrolled per-user in Azure Multi-Factor Authentication. If the user hasn't yet registered authentication methods, they receive a prompt to register the next time they sign in using modern authentication (such as via a web browser). Users who complete registration while in the Enabled state are automatically moved to the Enforced state.
So , in other words, you can set to Enforced and they should still be able to register per user before they can do anything else. Isnt that what you want?
If not, then you will need to set to enabled and then force them to use MFA in some other way ( See Conditional Access)
I would suggest simply telling them they need to register first and enforce that.