You have a SharePoint Server farm and a Microsoft 365 subscription.

You plan to migrate some SharePoint sites to SharePoint Online.

You need to identify users who have access to your SharePoint Server on-premises environment and are NOT mapped to a Microsoft Azure Active Directory (Azure AD) account.

What should you use?

A. The Test-SPContentDatabase cmdlet

B. SharePoint Migration Assessment Tool (SMAT)

C. SharePoint Migration Tool
D. Azure AD Connect

References:
https://docs.microsoft.com/en-us/sharepointmigration/sharepoint-migration-identity-mapping-tool