Hello @Pascal Altpeter to get the collection of bookingAppointment objects for a bookingBusiness, that occurs in a specified date range, you can send a GET request to the bookingBusinesses endpoint and get the calendarView for the date range as documented here:
GET /bookingBusinesses/{id}/calendarView?start={start-value}&end={end-value}
See sample request in graph explorer below:
Also, please note that Customer Booking is available in beta and these APIs are subject to change and not supported in production.
Thanks,
Diana (MSFT)