If Calendar service is configured to allow multiple customer to book for a service slot (e.g. workshop), it is currently impossible to obtain the customer list from Graph API for Bookings, Calendar or Events.
Without the ability to obtain this info through Graph API, automation through Power Automate will be impossible.
It is not feasible to expect booking service administrator to export the data file manually everyday to perform back desk processing. Please include this enhancement soon or we will be forced to move out of Ms Booking.