Using older versions of Outlook for Mac for personal email and calendar
Are you sure this will not work for you? I am an Admin at a college and it works for us, the problem does come back, however, it works temporarily.
I don't want my users in terminal, so I have them do the following:
With the Apple Calendar app open, open Activity Monitor, (make sure All Processes are listed under the view menu) search for CalendarAgent, select it and force quit (click the stop sign in the menu bar), in the pop up window, click force quit.
Quit Activity Monitor and the Calendar app, then open the Calendar app, wait a few and it should repopulate shortly.