multiple contacts cards across accounts duplicate
I sync my iCloud contacts and calendars including Google (though I only _use_ Google calendar). I now see up to three entries, apparently (1) Mac, (2) iPhone, and (3) a few from Google (didn't know I _had_ Google contacts). I cannot edit my iMac address book _at all_, i.e., edits do not stick, even with iCloud switched off. (In fact, I cannot even delete the cards!)
On the (mostly near) duplicate entries, contact changes propagate just fine from either Mac or iPhone. This set of contacts seems to operate entirely independently from my Mac version--it's also significantly out of sync. When I deselect the iCloud contacts and reconnect, saying 'yes' to merge, there _is_ no merge with my Mac contacts--the iCloud contacts just show up as separate cards. :-| I get a similar response when I check Contacts in my Google account (which is strange, since I do not keep contacts in Google--how did contacts propagate there?).
In Contacts, even when the cards are "true" duplicates across Mac and iCloud, they're not found. Linking Cards also does not work.
What I would like to do is merge all contacts and aggregate the information, since it appears that I have near-duplicates mostly. I don't have duplicate friend names (like most people), so I'm happy to aggregate based on name alone.
I am on Catalina 10.15.3, use iOS 13.3.1 using the same Apple ID everywhere. If it's useful: my Contacts list goes back more than a decade, but I have not ever seen duplicates like this since about the time I put my Desktop and Documents folders in iCloud (a clue?). Much appreciate ideas for this bewildering situation!
iMac 27" 5K, macOS 10.15