Thank you for posting this in Microsoft Q&A.
When you are migrating the MFA policy there is an option to select group to which you want to enable MFA.
Once the migration process is completed only those user or groups which you have selected in authentication method policies will get prompted for MFA. You can refer below article to migrate MFA and SSPR policies in Entra ID. Documentation links:
- How to migrate MFA and SSPR policy settings to the Authentication methods policy for Microsoft Entra ID: https://learn.microsoft.com/en-us/entra/identity/authentication/how-to-authentication-methods-manage
- Manage authentication methods for Microsoft Entra ID: https://learn.microsoft.com/en-us/entra/identity/authentication/concept-authentication-methods-manage
- Plan a Microsoft Entra multifactor authentication deployment: https://learn.microsoft.com/en-us/entra/identity/authentication/howto-mfa-getstarted
Let us know if you have any further questions.
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