WhatsApp on Windows computer app: camera does not work. How to fix?

Windows 10. WhatsApp app: When I start a video call, my camera's video is not transmitted. The camera does appear in the choose camera menu of the call-in-progress window. When I select this camera, a grey rectangle appears in the window. I guess the camera's live image was expected to appear in this rectangle. But it is just still-grey. When I select this camera. The camera's recording indicator light turns on, but no image appears in the call window. I guess this is not a matter of permissions, because the app does interact with the camera — it turns on the recording indicator light on the c

Question by Alexander Gelbukh on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.