On laptops, there's usually a light that turns on when the camera is active. I (like to) believe that this light is controlled by the camera's firmware, i.e., it can't be manipulated by software? Can someone knowledgable confirm this?
Hit and miss.
If it can be controlled by the camera's firmware, then it can be controlled by software. All it takes is a bug in the firmware, which is unlikely to ever be updated.
Some camera lights are controlled by the firmware, others are wired onto the data line, so the moment data is going either way, they light up.
However, defeating the light even in the directly wired case is possible, and has been done many times. If you fire up the camera, take a photo, and turn off quickly enough, the light won't be perceived by the victim. (I believe the FBI and the NSA both had tools that did this that became public knowledge a number of years ago).
FWIW, Apple system (OS) updates frequently include firmware updates, not only for the FEP/boot code but other devices as well, especially for security issues. Apple has been pretty good about this.
Not addressing the rest of your comment, just this one point.
PS: don’t know why the phones don’t have a similar indicator for “front camera on” and “speaker mode on”. BOM cost I suppose.
"We observed that, on average, fewer than half of our participants (45%) noticed the existing indicator during computer-based tasks. When seated in front of the computer performing a paper-based task, only 5% noticed the indicator."
- Somebody's Watching Me?: Assessing the Effectiveness of Webcam Indicator Lights - https://dl.acm.org/doi/abs/10.1145/2702123.2702164
https://support.apple.com/guide/security/hardware-microphone...
edit: seems I'm wrong from googling