Hello,
Calendar app contain a bug or error.
When I'm trying to add an event using "+ Add event" button, I get only this error in my console.log:
Uncaught TypeError: can't access property "hide", pa.getInstance(...) is null
Clicking on a random day and closing modal make "+ add event" button working again.
This issue is present on metronic demo website
https://preview.keenthemes.com/metronic8/vue/demo1/#/apps/calendar