Having it in the status bar would defeat the purpose as ill behaving actors could possibly circumvent this, having it in the hardware as a led would make this if not impossible most likely infeasible. I’ve only heard one instance where someone were able to go around the led and if I recall correctly that was on the old PowerBook and required physical access to flash the firmware on the camera hardware module with custom malicious firmware.

You can get that functionality with Microsnitch. It works for the microphone too.

I use MicroSnitch on my mac and love it. I just need it for the iPhone. It doesn't exist, does it?

No but it sounds like a good idea. I suspect it would require a jailbreak though.