@Christine N. Albanese Thank you for reaching out to us, As I understand you want to exclude users from the registration campaign to set up Microsoft Authenticator App.
Please refer to this https://learn.microsoft.com/en-us/azure/active-directory/authentication/how-to-mfa-registration-campaign#enable-the-registration-campaign-policy-using-the-microsoft-entra-admin-center:~:text=to%20three%20times.-,Enable%20the%20registration%20campaign%20policy%20using%20the%20Microsoft%20Entra%20admin%20center,-To%20enable%20a where you will find Excluded users and Group option - Allows you to exclude different users and groups that you want omitted from the feature. If a user is in a group that is excluded and a group that is included, the user will be excluded from the feature.
Also you can use this option to change the state from Microsoft managed to Disabled ( to disable the registration campaign).
Let me know if you have any further questions, feel free to post back.
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