Thanks, tried that, nothing changed.
This all came to light because I was curious as to why some contacts showed up in my email client (Postbox, which is tied into both my Yahoo and Google mail accounts) but not on my iPhone. Started poking around and made the discovery that in the System Preferences “Internet Accounts” location, neither the Yahoo nor Google accounts were listed. Added them both and then cleaned up whatever duplicates there were. I now have exactly the same number of contacts on my iPhone as I do on the 2014 Mac mini, as I do on the 2020 MacBook Pro M1. So, not really experiencing any issues or data loss, just a simple curiosity.
I ended up putting all my contacts into iCloud during the cleanup process, maybe I’ll try taking a few contacts out of iCloud and put them into the Yahoo and Google accounts and see if that changes anything.