If you have an internal user showing as ExternalAzureAD (or federated), you likely need to reset the redemption status with the correct user email added to the internal user object.
To resolve this you can use the Graph Invitation API, add the external address to the user's account, and then reset the invite status following this guide:
https://learn.microsoft.com/en-us/azure/active-directory/external-identities/reset-redemption-status
Note that in order to delete an external user you need to have a role assigned that has permission to delete users, and some user types can only be deleted by Global Admins or Privileged Auth Admins. https://learn.microsoft.com/en-us/entra/identity/role-based-access-control/privileged-roles-permissions?tabs=admin-center#who-can-perform-sensitive-actions
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