Same issue with my MacBook Pro 2017 (two Thunderbolt ports), camera stopped working at some point after moving to Big Sur. Current version macOS Big Sur 11.5.2 installed.
Tried various workarounds (e.g. here: https://piunikaweb.com/2021/03/15/macos-big-sur-camera-not-working-issue-and-its-workarounds/) to no avail.
Camera is still listed in the system hardware:
FaceTime HD Camera:
Model ID: Apple Camera VendorID_0x106B ProductID_0x1570
Unique ID: [ID HERE]
I find the story that it is hardware failure (mentioned above) completely unconvincing. Too many people reported this at the time of Big Sur update, which clearly points to software / update as the reason for the issue. I urge Apple to give this proper attention, especially as the camera became an important piece of hardware in recent past (maybe you guys heard of that virus that is on the news every now and then?). This is not so old equipment, also, and I've never seen any break in any of the laptops I was using before.
If Apple cannot fix the software soon and keeps telling us it's hardware without giving good explanation, for me it smells like cover for software engineers not wanting and/or being able to fix the issue that they have created. Then I'll consider my next purchase very carefully. I've heard that competition's cameras work fine.