Do you see a red error message that looks like the below image?

If yes, Shutdown and restart your computer. This will fix 99.9% of all issues.

Have you used Zoom, Skype, or any other video app recently? Some poorly written applications on a computer can restrict access to the camera, so make sure to close any application that might already have that access, for example, Skype / Zoom, video editing software, etc. When these apps restrict access to your mic and camera, you need to restart your device to fix the issue.