<aside> 👇 Please note that this a workaround for setting all new Calendar events to private as default, as there is no setting in Outlook to control this.
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Open Outlook and go to your calendar, create a new event, and enable the Private option
Publish this new appointment as a form in order to create a template – to do this go to the Developer tab, click Publish, then Publish Form As (If the Developer tab is not visible in your Outlook, turn this on via File > Options > Customise Ribbon > Main Tabs > tick the box for Developer)
In the Publish Form As window, set the Look in: dropdown to Personal Forms Library, enter a “Display name:” and “Form name:” for your form (/template) and click Publish
Go back to your Calendar view, right click on your calendar and choose Properties