Yeah, I did have older versions on my computer. Didn’t know that was a problem.
And you’re right. My computer is still running v2.81a. I had just assumed, after going through the normal update process, everything was working.
So I deleted all the old versions, and then reloaded 2.91.0.
But opening Blender, it still ran the 2.81 version.
So now the problem is, “Why hasn’t my computer updated Blender since 2.81a despite my having my haveing downloaded several newer versions?