Upgrade to Big Sur Duplicated Contacts on Google

I upgraded my iMac from Mojave to Big Sur on October 2 and now all my 6,000+ contacts appear to be duplicated. (I skipped Catalina altogether because it did NOT appear as an option on System Preferences > Software Update.)

The recommended fix I found for this is to restore a Contacts backup from iCloud:

https://www.idownloadblog.com/2021/01/22/fix-duplicate-contacts-icloud-big-sur/

Unfortunately, I don’t backup my Contacts to iCloud—I sync Contacts among my Apple devices via Google Contacts—so I don’t have an archive to restore.

The last change I remember making to Contacts (on my iPhone 12 Pro running iOS 15.0.1) was October 2 mid-morning. I upgraded my iMac to Big Sur October 2 mid-afternoon. I presume that the changes that I made in Contacts on my iPhone would have synced iPhone <-> Google within this several-hour period.

Details:

1. iCloud: I logged into iCloud (https://www.icloud.com/contacts/) and see no duplicates but it has a count of only 4,882 entries and several changes I made the morning of October 2 on my iPhone are NOT reflected here. There are NO archives listed on iCloud (https://www.icloud.com/settings/).
2. iMac: I opened the Contacts application (ver 13.0 2452.7). When I select the “Google - All Google” tab, it says there are “11,934 Cards” and they all appear to be duplicated. When I select the “On My Mac - All on My Mac” tab, there are 4,937 Cards and none of them appear to be duplicated. When I select the “Directories - Google” tab, no contacts are listed. When I select the “Smart Groups - Last Import” tab, only one contact is listed, mine; it says “Siri Found in Accounts.”
3. Google Contacts: When I log into my Google Contacts (https://contacts.google.com/?hl=en), it says that there are 12,019 contacts and all of them appear to be duplicated. It offers to “Merge & Fix” 2,973. I used to have just over 6,000 contacts in Google, so the total seems reasonable—except for being an odd number—if they were all duplicated. The "Merge & Fix number seems way too low so I’m hesitant to try it.
4. iPhone: Contacts on my iPhone all appear to be duplicated and the count is 12,035, slightly more than on Google but still odd.

Why did upgrading macOS duplicate my contacts on my iPhone (and Google)?!? I do NOT use macOS Contacts and I do NOT sync them to ANYTHING, not even iCloud.

Does anyone have any advice on what do do next?

Thank you.