You can hide and unhide events on the calendars app - this is useful for when you'd rather keep a specific calendar personal/private, or for when you accidentally create duplicate calendars on iCloud.
Hide and unhide calendars
Go to the Calendar app
Select View > Show Calendar List
Select or deselect the calendar's checkbox in the Calendar list to show or hide a calendar's events
To show or hide events from all calendars, press the Command key while you select or deselect any calendar's checkbox
Hide or unhide Holidays and Birthdays
Select Calendar > Preferences, then click General
Select or deselect Show Birthdays calendar
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