"The server responded: “403” to operation CalDAVAccountRefreshQueueableOperation."

I just logged into iCloud to check because of your message, and sure enough, I'm getting an error there too:

Couldn't load events. New events couldn't be loaded because of a server error. Please try again.

I'm having the exact same problem. I've tried deleting cache files, restarting, toggling the calendar off / on, and completely logging out of iCloud and back in again. Nothing working.

MacBook Pro (13-inch, M1, 2020), with a Family iCloud plan, with six calendars.

Yeah, I couldn't even check off a notification on the calendar because of the same reason. I'm M1 MacBook Air 2020. But the same is happening on my iPad, iPhone etc. Hopefully it's an iCloud problem which is resolved in the next few days, until then I'll have to revert to pen and paper calendar!!!!

Same here, tried logging out of iCloud, happening on and off on all devices but mainly Mac.

Glad it is not just me. I've opened a ticket with Apple Support and they are getting back to me later this week. For me it does not work perfectly on iCloud.com and I get the exact same error messages periodically

me2. computer calendar doesn't update to iPhone