Many tablets have a good feature: autobrightness. They use integrated cameras to check lights level.
Every laptop have camera but Windows can't use this cameras as light sensor.
Such functionality doesn't need to everyone so there are no need to integrate this feature in Windows core but this can be realized with PowerToys as a real toy. This toy can auto-balance brightness by checking external light levels.
Most laptops actually can set screen brightness. I am not sure if they use the actual camera to accomplish that as well versus a light sensor.
Is this for like a desktop scenario?

Not every laptop have such a feature. For example - my 2019's Lenovo Legion doesn't (and his camera not even supported by Windows Hello). Only Night Light, HD Color and scaling.
For such loosers this toy can be a salvation as an external solution for oficially not supported hardware configurations.
A few ideas...
This means the camera has to be open either continuously or a short time in regular intervals. Does that not use more power?
Also, (my experience is) the camera usually can only output to one program at a time. What if the camera is already in use for a video call? Or the other way around: if this new function blocks access from other programs? Although it is possible with software (maybe the new driver that's included in the latest PT version?).
What about the cam-on indicator light - if present? If it's always on (even though the user is not really using the cam) then the security factor of this light is being undone. A flashing light might be considered annoying or just confusing.
Speaking of security, some people want to keep the camera covered (with black tape or something) when they are not using it.
As both of you said, cameras can be quite different in capabilities on different devices: with or without a simple brightness sensor, IR sensor (for Hello) and indicator light.
while interesting idea, i don't seeing the PowerToys team building this idea out. It has a ton of permutations of complexity.
Most helpful comment
A few ideas...
This means the camera has to be open either continuously or a short time in regular intervals. Does that not use more power?
Also, (my experience is) the camera usually can only output to one program at a time. What if the camera is already in use for a video call? Or the other way around: if this new function blocks access from other programs? Although it is possible with software (maybe the new driver that's included in the latest PT version?).
What about the cam-on indicator light - if present? If it's always on (even though the user is not really using the cam) then the security factor of this light is being undone. A flashing light might be considered annoying or just confusing.
Speaking of security, some people want to keep the camera covered (with black tape or something) when they are not using it.
As both of you said, cameras can be quite different in capabilities on different devices: with or without a simple brightness sensor, IR sensor (for Hello) and indicator light.