I found a workaround that fixes the issue and I wanted to share it. My computer is a 5K iMac. I had (but was not using) a small program called QuickRes that allows for a wide variety of screen resolutions. Apparently, Apple uses a technique called HiDPI (high dots per inch?) that normalizes the high res screen to adjust objects and texts to a usable size.
The HiRes program allows the same resolutions both with and without HiDPI. Use it to go to the same resulution your screen was set for but without the HiDPI. The photo enhancement in Library will be fixed. So far, I have not run across problems with the HiDPI turned off.
It's possible that my very recent update of the OS to Catalina 10.15.7 might have altered the graphics accelerator somehow. In any event, it works for the time being. Thanks.