Hello William M.,
Thank you for reaching out to Apple Support Communities.
These steps may help:
"Check your default Calendar, Reminders, and Contacts account
If you store and edit your events in iCloud instead of another place, like On My Mac, Exchange, or Google, then iCloud automatically updates your calendars. If you use multiple accounts on your Mac like iCloud, Gmail, and Yahoo, make sure that iCloud is your default Calendar account:
- Open the Calendar app.
- Choose Calendar > Preferences.
- In the General tab, make sure that one of your iCloud calendars is the default.
If you store and edit your contacts in iCloud instead of another place, like On My Mac, Exchange, or Google, then iCloud automatically updates your contacts. If you use multiple accounts on your Mac like iCloud, Gmail, and Yahoo, make sure that iCloud is your default Contacts account:
- Open the Contacts app.
- Choose Contacts > Accounts.
- Click the iCloud tab and make sure that you're signed in with your Apple ID.
As long as you've turned on Reminders in System Preferences, your iCloud reminders appear on your Mac."
More details can be found here: If your iCloud Contacts, Calendars, or Reminders won’t sync
If the issue persists, attempt to test in a new user account to see if the same thing happens.
Cheers!