Thank you for replying. The next morning when I started up Opera again, Duck Duck Go was the default search engine. Not sure what happened, as I had tried many things -- relaunching in safe mode, switching to Google (Opera's default) and then back to Duck Duck Go, closing Opera and re-opening, etc.... but it's all working fine now.

I have set Duck Duck Go as my default search engine, but Opera defaults to Google at start up and in new windows / tabs. I have tried Bing also, but it still defaults to Google. Any advice on how to get Duck Duck Go to work as my default appreciated.
Mac OS 10.14.6
Opera 65.0