Hi Tonti,
Thanks for reaching out.
As per my knowledge there are no such APIs, publicly available to list out all the appointments of a user in Bookings calendar currently.
Since this feature/functionality is presently not available, you can submit a feature request idea using this support link, which will be monitored by Microsoft team and make the enhancements to Microsoft Graph APIs. I will also upvote for you.
Hope this helps.
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