Have played with it some more, and I think gotten it to
work. This is a very new Mac and nearly the latest OS (Big Sur just came out yesterday, I have the latest Catalina).
I rebooted and reset the graphics card, which seems to have fixed the zooming issues. But it also got rid of several chart libraries, though not all. Rebuilding did some good but others had to be removed and reinstalled. There are other things that seem gratuitously different, like opening the properties dialog in waypoints brings up a mini window that must be expanded to see everything, every
single time it is opened. But at least I've gotten it to
work a bit.