Apple devices synchronize calendar subscriptions with their iCloud service. Usually this works automatically and well.
Sometimes this synchronization fails. When you delete a subscription, this deletion is not sent to iCloud, so iCloud does not know about it. When the devices download the current status of iCloud calendars, the deleted calendar is still there, and it reappears.
Since the issue is with iCloud, it can't be fixed by WebCal.Guru. Please try the following in order.
Reboot the affected device.
To do this, open the menu and select Restart…
After the Mac has rebooted, try to delete the calendar again. If the issue has not been fixed, please continue to the next step.
If rebooting did not fix the issue, next we'll try logging out of iCloud and then logging back in.
Open the menu and select System Preferences…
Click Apple ID.
Click Overview.
Click Sign Out....
You do not need to keep copies as we'll be logging in very soon.
Click Continue.
Now you've logged out of iCloud.
Next, log back in with your Apple ID.
Then try to delete the calendar again.
Updated Wed, 08 Feb 2023 12:08:23 +0000 UTC