This used to be a thing, where you’d flash the LED briefly and hope the user didn’t notice. But new Macs prevent this by having a minimum duration the light will remain on.
FWIW I tried using the command line utility isightcapture on my 2019 macbook, and the LED turned on for 4-5 seconds and I got a dialog asking if I wanted to allow access to the camera. So this seems to be true.
I still have a camera cover though
Hm, seems like the LED has some logic to it and isn't just connected directly to the camera....