Using Get Event Graph API GET /users/{id | userPrincipalName}/events/{id}
you can get Event details in the user's mailbox. Please refer to this documentation for more details.
You can also use CalendarView Graph API GET /users/{id | userPrincipalName}/calendar/calendarView?startDateTime={start_datetime}&endDateTime={end_datetime}
to Get the occurrences, exceptions and single instances of events in a calendar view defined by a time range. Please refer to this documentation for more details.
As you have mentioned about 'unscheduled items will not appear there either' can you elaborate more on that.
Hope this helps.
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