On Apple devices, the browser must be granted access to the camera and microphone in the macOS System Preferences under Security & Privacy.
On Windows, the activation of the camera or microphone for the browser may have been disabled by the system administrator on a company laptop.
Perhaps the wrong input has been selected. Here is a self-test for microphone and camera – your own image must appear and your own audio as an echo.
The web browser also has settings for managing camera and microphone permissions. In the Brave browser, for example, this can be found under "Privacy and security/Site and shield settings/Permissions/Camera or Microphone". In other browsers such as Firefox, Chrome, or Safari, these settings can be found in a similar location.