@kmara I couldn't agree more--there's no excuse for this kind of botched "upgrade". They've been around long enough to know and do better.
I finally managed to do the roll-back, and have both copied my data into several spots and imported it into Vivaldi. This didn't give me back my tab system, but better than nothing if Opera fails again. Plus I'm copying some of the most essential into Vivaldi, which I hope won't lose them.
It's ridiculous that I now have four browsers installed--Opera, Vivaldi, Firefox and Chrome. I refuse to use Edge, it's horrible--much worse than IE ever was & it was no great shakes.
Now, let's see what happens when I try to open Opera tomorrow. Nothing dire, I hope. Lost time that could have been much better spent than doing this.