Hi,
Let’s make sure the issue is isolated to Facebook or if it’s a system wide issue.
In the search bar, type Camera and press Enter. Is your camera working there?
If not, can you please describe what you see on the screen and provide any error messages or error codes?
What is the make and model of your device?
In the search bar, type MSINFO32 and press Enter. Please share a screenshot of that window.
Are you using a built in camera or an external one?