In your Opera’s toolbar, go to Tools/Advanced/Cookies, scroll thru all of the entries, and delete *everything* related to Google/Chrome etc. Many of the condensed [+] cookies need to be opened so you can delete each entry, or some might survive. In recent Opera versions, deleting the main entry does it; older versions required deleting all entries under the [+]. It changes to open when you see [-].
Keep scrolling and delete all of the various website entries for Google/Chrome etc, too. You’ll be stunned at what’s in that Cookies drop-down menu.
What version are you using? It’s in the toolbar under Help/ About.
I was stunned. Yes. Thanks.