Archive Calendar events by year

"Apple Calendar storage is full - how can I export previous entries by year / date range please?

Today Apple Calendar (previously iCal) has stopped letting me add entries and stopped syncing with iCloud across my devices.

It appears I have reached the limit of the number of entries I am allowed in Apple Calendars (see Limits for iCloud Contacts, Calendars, Reminders, Bookmarks, and Maps - Apple Support)

(small exclamation marks by some of my calendars say "There is insufficient storage space for “Particular Name of Calendar” in account “iCloud”.)

I would like to keep an archive of my previous entries over the years before deleting them - by year / date range rather than the whole Calendar in one, across all my different colour coded calendars. Can anyone advise me how I can do this please?

Thanks"