I don’t know how it behaves on ARM (so Apple’s SOCs or your phone) but on Intel or AMD there are two manifestations:
They can intercept data and manipulate memory, and that’s pretty much transparent, you wouldn’t know unless you were a very advanced user running specific tests.
Or they can literally just brick the chip. It blows a few electronic fuses and corrupts it’s own firmware, you press the button to turn on the device and it doesn’t respond and will never respond again. Those fuses are permanent, once bricked its gone.
I don’t know how it behaves on ARM (so Apple’s SOCs or your phone) but on Intel or AMD there are two manifestations:
They can intercept data and manipulate memory, and that’s pretty much transparent, you wouldn’t know unless you were a very advanced user running specific tests.
Or they can literally just brick the chip. It blows a few electronic fuses and corrupts it’s own firmware, you press the button to turn on the device and it doesn’t respond and will never respond again. Those fuses are permanent, once bricked its gone.