I've been using Opera as a sole browser for many years now, to the point I cannot remember using another browser for anything other than when a website doesn't like that I'm not using either Safari or IE.
Late last year, after updating to Sierra, Opera started freezing up the computer. I leave everything on including the two browser windows with six to eight tabs in each. Been doing that for some years without issue until then.
Two/three days ago I updated OS X with a security patch. Now Opera starts and within less than a minute the beach ball starts spinning. Not on any pages, not going anywhere, just on the start screen with the meteors falling towards Earth, the meteors freeze and Opera is dead. I've left the beach ball spinning all night and it is not any better in the morning.
That was on my iMac. Now I'm starting to see that same behaviour on the Mac Pro, Macbook Pro, Mac Mini (both of them) and I'm a bit hesitant to upgrade the Macbook Air.
There's no sense even trying to reinstall Opera until this is fixed. It doesn't work.
I'll have OS versions this weekend (I'm at work now). Can't give you the Opera version number, it can't stay open and functional long enough. I know I updated it last week, though.