"All Apple silicon-based Mac notebooks and Intel-based Mac notebooks with the Apple T2 Security Chip feature a hardware disconnect that disables the microphone whenever the lid is closed. On all 13-inch MacBook Pro and MacBook Air notebooks with the T2 chip, all MacBook notebooks with a T2 chip from 2019 or later, and Mac notebooks with Apple silicon, this disconnect is implemented in hardware alone." [1]
[1] https://support.apple.com/guide/security/hardware-microphone...
That's what they said about the first gen Facetime cameras. "oooh don't worry, it's controlled in hardware!"
We have no way of verifying that anything they said in that document is true.
It's clear Apple define "Hardware" as "Not using the main CPU". They've pretty much admitted it's firmware based, otherwise the T2 chip simply wouldn't be involved to be mentioned.
The T2 chip is mentioned in the quoted passage as an indicator of the architecture version, not necessarily an indicator that the T2 chip is directly involved
Obviously the camera is also 'disabled' when the lid is closed regardless of the controlling circuitry. So while that's a good feature, it's not relevant.