Hi,
I am curious about following statement : When I use the Calendars.ReadWrite, consumer users are automatically prompted to grant access (user consent), but enterprise users are shown "Need Admin Approval" when trying to connect.
Do you mean B2B (GUEST ) users are able to provide consent for Calendars.ReadWrite while member users of that AAD requires admin consent ? If this is true, did you review the recent preview for consent and permissions ? You can now control which permissions can be forced for admin consent while allowing low impact permissions with user consent.
Let me know if this helps !