MacBook Air camera's not working When I turn on the Photobooth or Zoom app, the green light keeps on blinking and the screen just shows gray color. What to do?
A blinking webcam light means there’s a fault with your webcam.  It could range from a simple hang up of the hardware or driver to an out of date firmware update or the webcam has failed altogether.

The first thing you want to do is reboot.
If the issue still persists, reboot in Safe Mode (hold Shift while booting).  This will make it so only Apple drivers and software is loaded to remove possible conflicts
Make sure your system is fully up to date
Run Apple Diagnostics (hold D while booting)
Try a USB webcam.  If you get to this point and the USB webcam works, it’s a hardware failure of the webcam itself. You’ll have to decide if you want to replace the webcam which requires disassembly of the display or get use a USB webcam.