I right-click or double-click to create a new event or edit an existing one. I don't think a single click has ever opened one.

JosephScarano said

Starting Monday, 7/10 I can no longer click on a date in the calendar to add an event. Also, I cannot open and edit any existing events in the calendar. The only way I can add an event is to go to the menu, select Events and Task and add a new event.

Thanks, that worked. But in the past I was able to double-click on the date or an existing event to add or edit.

I can no longer open an event to edit it or view the details. I tried right clicking but Open is greyed out.