Before diving into complex software fixes, one must rule out physical obstructions. Many modern laptops include a physical privacy slider above the lens or a dedicated function key
: Look for a camera icon with a red cross in your browser’s address bar. Click it and select "Always allow https://meet.google.com to access your camera" .
Are you seeing a specific , or is the screen just black ? Knowing your operating system (Windows, Mac, or ChromeOS) can also help me provide a more specific step-by-step fix. Troubleshoot camera issues in a meeting - Google Help