The best thing to use is "Magic Tape" to cover your camera. It adds a frosted window effect while not disturbing your screen's brightness adjustment feature.
I did helpdesk during the pandemic and the number of tickets for "poor microphone quality" was insane. Most people used tape or bandaids to cover the camera... And microphone
The real reason for shitty microphone quality is using the shitty microphone that comes with your laptop. Get a decent wireless headset with a mute button on it and you can move around your house during meetings while still sounding way better than you would be sitting in front of it using the laptop mic.
Yes. Usually you have a brightness and sometimes also a proximity sensor. Proximity is usually used for phones so they can deactivate the screen if you hold the phone like an actual phone against your ear.