Quite the contrary, I think you DID help!
Had you not replied asking me to be more detailed John may not have replied.
Thank you very much for responding!
By the way, I have three Macs, one with High Sierra, another with Mojave, and another with Catalina. Based on John's reply I thought I would experiment. I turned iCloud Contacts OFF on each Mac, and "On My Mac" was created. I added a few contacts to that and then turned iCloud Contacts back ON to see if they would merge. Here's the result;
On the High Sierra Mac the On My Mac section remained and my contacts stayed there and were not merged, which is what I was wanting.
On the Mojave Mac, when I turned iCloud Contacts ON a popup told me the contacts would merge and offered a Merge and Cancel buttons. If I didn't want to merge my contacts and clicked Cancel then iCloud Contacts remained OFF and On My Mac was the only place to store contacts. If I clicked Merge then the contacts were merged with iCloud contacts and "On My Mac" was removed.
On the Catalina Mac when I turned ON iCloud Contacts the contacts in On My Mac were merged, with no popup appearing giving me an option, and the "On My Mac" section was removed.
Thanks again for the reply!,