1. Polarizing Filter
An LCD screen uses polarized light to produce images. So a polarized filter over the web camera can block reflections from the screen. The clip-on lens kit I purchased has a polarizing filter, but this was not designed to be used in conjunction with the zoom lens. So I unscrewed the ring holding the polarizing filter in place and inserted it in under the zoom lens. This greatly reduces reflections. Those using DSLR cameras as web cameras will be able to purchase polarizing filters for these.
2. Custom Spectacles
3. Dark Theme
In addition, I have found that a dark theme on the computer desktop helps. This has a black background with white text, so the screen emits much less light. How this is set varies between operating systems, and browsers.
Zoom will go to dark theme, when this is set in the Microsoft Windows, or Apple OS operating systems. However, this doesn't happen with Linux (which I use), or with Android. I have suggested Zoom fix this. It could be rectified by having Zoom follow the operating system theme, or if that is not possible, add a manual setting. Or, Zoom could simply decide to make a dark theme the default for the Android and Linux versions.