The process is very simple, but depends on whether they're local or cloud/server events. I use Outlook 2016 (Win) for my business items, iCloud for most of my personal stuff AND as a cloud-based back up for my business items, along with a local archived copy. The key to moving from Win Outlook is to not use the "Export" function (which result in PST files), but rather the "Save As" function for your Calendar(s) to get the desired iCalendar file(s). Importing the resulting file into Apple Calendar is a simple. The process of saving Outlook Calendars has been pretty much the same since Outlook 2007 AFAIK.
In Win Outlook, in the Viewing Pane, select the calendar you want to save. Then, using the File Menu select the Save As option and you'll be presented with dialog boxes that will result in an .ics iCalendar file. Be sure to select the appropriate date range - I generally make the whole calendar my target as I make iterative, cumulative backups, but I'm assuming you're looking to do this once. Select the options you want in the dialogs, then save the file - that's it!
In Calendar, I recommend setting up a new calendar prior to the following importing procedures - name it as you see fit. In Calendar, you can either drag the resulting ICS file to the Calendar icon in the Dock, or use Calendar's Import Command and navigate to the ICS file. You'll be prompted for a calendar to import the items into - choose the calendar you want to import the events into, and import them. And, that's it.
I've had zero issues with this "Save As" and "Import" workflow, going back several years. I verify my event milestones and preferences - alerts, number of recurrences, dates/times - it just works...
The alternative to getting your events out of Outlook is to drag ............................... each .................... of .......................................... them .............................................. to .............. the ....................................... Desktop ................................................... and ............ dragging .............. them ................................ to Calendar ......................... Buy lots of booze first if you're going to do it this way!
