Icloud backup Calendar

See the article Delete a calendar on iCloud.com - Apple Support

Restore your calendars and events on iCloud.com - Apple Support

The calendar is erased after 30 days and can't be recovered .

HelpRestorecalender wrote:

I need to restore calendar from over a month ago--- as I deleted an event I need to check on. The list to restore only shows a few weeks back. Where can I

find older dates to restore to?

Use iCloud.com to restore and recover iCloud information - Apple Support