Thanks @burnout426,
Before I saw your note, I found another note from a Monterey user who had the same old version of Opera that would not update. They pointed to
https://get.opera.com/ftp/pub/opera/desktop/ where they said they could find more recent versions.
So, from that page, I installed Opera version 90.0.4480.84. (Sidetrack: I first installed version 100, and went to the Chrome webstore. The "Install to Chrome" button was not greyed out, but when I used it, I got some kind of System Data Error. So I tried v90. I figured it might take a few installation cycles to find a version that worked.)
Opera v90 installed fine. I went to the Chrome Extensions and again the "Install to Chrome" button was active. This time it worked and I was able to install the extension I wanted.
Then Opera popped up a new page saying I'd been upgraded and apparently it had automatically upgraded me to v126, which appears to be working fine as well.
The bug was in v83, which erroneously told me I was up to date and thus would not upgrade me. You may be right that an old API that didn't receive the correct information may be the actual source of the error. But I'm not going to chase it. I'm at 126 and I have my extension loaded.
Thanks again.
