Calendar App Crashes on Opening After Upgrade to MacOS 15.0.1

This just worked for me - read off of Reddit:

I was able to fix this on the mac by turning off calendar syncing in iCloud under System Settings.

System Settings -> Internet Accounts -> iCloud in the "Save to iCloud" section select "See All" and then turn off Calendar.

Calendar should be able to open up without crashing. I'd wait like 10 minutes and then turn the iCloud syncing back on (if you want). Then just close calendar and re-open to make sure that it doesn't crash again.

Everything works now.

You can try this

Open Terminal -> softwareupdate --fetch-full-installer --full-installer-version 15.0.1 and then run /Applications/Install macOS Sequoia over the top of your existing installation.

I've tried all the suggestions apart from a full reinstall of Sequoia - including removing subscribed calendars - and no luck. As soon as the iCloud sync is turned back on it lasts for about 15 seconds before crashing out.

I only have a couple of ical calendars so not much option for turning them off if I actually want a useful calendar :-(

Really, really unimpressed with the level of quality coming out from Apple at the moment

I am experiencing the same issue, however mine seems to be linked to my external monitor (Dell S2421HN). If I open the calendar app on my main screen (MacBook) it works fine. As soon as I drag the app to the external monitor, then the beachballs twirls for about 5 seconds and the app crashes (producing the error log). If I reopen the app on my main screen it opens / works fine again.

Boot your Mac into Safe Mode

Start up your Mac in safe mode

Start up your Mac in safe mode - Apple Support

See if it can help clean up your Calendars problems.

Well that worked until It didn't....