Completed activities in the Week View or Day View of the main calendar can be hidden in the "More" menu options of the main calendar.
By design, completed activities in the calendar are shown with colored diagonal lines.
This can cause a challenge if there are several activities on a given date. To provide a solution for this challenge a CHECK can be placed in the "Hide Completed" drop down options of the "More" button.
This will "Hide" all completed activities from the Week View and Day View instead of showing the diagonal lines to provide a cleaner view and prevent items from accidentally getting missed when there is a large number of activities.
If need to see the completed items on your calendar then UNCHECK the option to once again view the completed activities as diagonal lines.
See video below for actual use: