Please note that you cannot manually create the events based on iCalendar source. The iCalendar events are created automatically based on iCalendar feed.
For instance, you would like the US Holidays to be shown on your Work Time Tracking Calendar. For that, you’ve added and configured iCalendar source, using a file.
As you can see, you cannot create the events “US Holidays“. The events are coming by iCal feed. The same if you are using the option URL, during iCalendar source configuration.