Further info. I have been away from my own computer and Zoom for about two months, and somehow in that the time the settings for camera and microphone were changed. When I bought this Windows computer, it had no camera but it did have Realtek hardware for sound. When Zoom came along I had to buy a combination mic and camera by Logitech, so my mic settings had to say Logitech. Somehow in the two months I was gone recently, the setting changed to the default, and everybody got confused.

Why did I buy a mic when I already had a mic? It was the middle of Covid, I needed a camera to start using Zoom, and hardly anybody had cameras for sale. I bought the one I could get, and it came packed with a mic. As I mentioned, it would have helped if I could have seen the brand name on the camera.

I did so many things I can't tell anybody how to repeat my steps, but if you are ever having problems like this, the first thing to do is to click on the itty-bitty picture of a loudspeaker on your tool bar. If that fails, find Control Panel and start wandering. Pack a sandwich and a canteen.