Found this on another forum...worked like a charm. Will still check out Vivaldi and thanks for that recommendation.
I found a way to disable the auto-update feature in the MacOS version of Opera.
If you wish to do so follow these steps:
1] Go to the Applications folder and click on the Opera.app while simultaneously pressing the "Control" key you will get a pop up menu. From that menu, select "Show Package Contents" which should be your second option.
2] Then a window opens with a folder that says "Contents." Open that and then you will see a bunch of files and folders.
3] Open the folder that is labeled "MacOS." Inside you should find a set of "exec" files. There is one called "opera_autoupdate"
4] Rename that to "opera_autoopdate," (just one letter wrong so you can change it back if so needed) and then closed everything and launched Opera as usual.
When I opened the opera://about page the app said it was checking for updates for about 5 minutes then displayed "An error occurred while checking for updates."
The app behaves normally in every other way.
So apparently I accidentally found the way to disable updates on the MacOS version of Opera. I was just fooling around and didn't think it would work, but it does.