Thanks for your reply 🙂
Wrt to the crash, I had a Time Machine backup from a few days earlier. I restored my mail folders by restoring /Users/myname/Library/Application Support/Opera/Mail from that backup. I restarted Opera 9.62.. no change, it crashed within a minute or two. I restarted and the same happened. However, I realized I was selecting one of the 'continue' options from the startup dialogue. When I restarted and didn't choose continue but started a new session, it stopped crashing. I then restored again from a more recent backup and I'm up and running again. Possibly for another 5+ years 🙂
I looked at upgrading opera a few years ago and the process screwed up, as I remember. 9.62 works just fine on a desktop for me with all the filters etc I have set up. I'll probably take your advice and try 12.15 at some point, though, I have another mac I can try on (not that I am paranoid or anything). Meanwhile 9.62 survives another day...
Cheers
E