Contacts in iCloud will not sync on my iMac

I was having what sounds like a similar issue, and similarly not having any success with the support recommendations since it seemed like everything was set to sync--BUT IT WOULDN'T!

I stumbled upon a reddit thread and was able to identify the problem. Here's the info in case it's useful and link to the thread below that.

"Go to Settings App, then > Contacts. If there is an entry called "Default Account", be sure to choose iCloud.

When I logged in my Gmail account, my Default Contacts settings become Google and I was having a similar issue to yours. It took me quite a while to figure out the problem :)"

https://www.reddit.com/r/MacOS/comments/e847vj/contacts_not_syncing_from_iphone_to_mac/fohhu2j?utm_source=share&utm_medium=web2x

Hello jasperjasley,

Thank you for using Apple Support Communities! I understand that contacts on your Mac are not syncing with iCloud. Since you're still experiencing the issue after following the steps in If your iCloud Contacts, Calendars, or Reminders won’t sync - Apple Support, you'll want to reach out to Apple Support using the link in this section:

"If you still need help

If you still need help, contact Apple Support. You can also use these steps to remove duplicate contacts or calendars."

Take care.