How do I resolve excessive calendar entry duplication on my MacBook Pro?

I can't seem to find any helpful advice on this issue other than 'delete duplicate entries by hand', so here goes. I have been experiencing some nightmarish issues with my calendar (Apple MacBook Pro running Sequoia 15.7.2). Entries are being duplicated three or more times. See screenshot attached. The calendar is virtually unusable. I haven't the time to delete every duplicate entry by hand each day, then delete it again when another copy appears.

I've checked that I'm not double-subscribed to any calendar, I've refreshed the calendar several times, signed in and out of my Apple account on all devices, etc. This is not a problem I used to have before. I do have two other devices that sync with my MacBook, an iPhone and an iPad. But I have had additional devices for years without ever seeing something like this. If anyone has managed to solve this problem, I would be grateful to know.

[Re-Titled by Moderator]

Original Title: Duplication issues--calendar