You can't move a meeting between calendars in Outlook for Mac
Original KB number: 2803557
You cannot use Microsoft Outlook 2016 for Mac or Outlook for Mac 2011 to move a meeting by dragging it from one calendar to another. Also, there is no Move or Copy option available to move meetings from one calendar to another.
This functionality is not supported by Outlook 2016 for Mac or Outlook for Mac 2011. This is because moving a meeting from one calendar to another might trigger discrepancies between your instance of the meeting and the information that the meeting organizer or other attendees have. In such a scenario, you might miss important updates sent by the meeting organizer.
While you cannot move meetings between calendars, you can move appointments in this manner. A Meeting is a calendar item that has attendees, while an Appointment is a calendar item that does not have any attendees and is on your Calendar only.