How to get events created in Calendar on iMac to sync to iCloud?
No event I create in Calendar on my iMac will sync to iCloud, thus those events do not appear in Calendar on my iPhone, iPad or iCloud.com. Events created on my iPhone and iPad do sync to iCloud properly and show up in Calendar on all devices including the iMac. Contacts I create on my iMac sync normally, so this problem is isolated to the Calendar app on the iMac.
I am signed in with the same Apple ID and password across all devices. All calendars shown on the iMac match those in iCloud and the other devices. I have tried unchecking and rechecking Calendar syncing in iCloud Preferences. I have tried signing out of iCloud on my my iMac and signing back in. None of those steps solved the problem.
What could cause the inability to sync new events created from only the Calendar on the iMac not to sync to iCloud?
What other steps could I try to fix the problem?
FYI, I'm running macOS Mojave 10.14.5.