>These usually get neither an LED nor a switch
Lots of ThinkPads have «Microphone is muted» LED. Not exactly what's requested (and is bound to a software mute/unmute shortcut), but it's better than nothing regarding state of machine being observable with a quick glance.
That one seems to be software controlled. I'm fairly sure I remember having the mic working with the mute LED lit, which was confusing. That was on a x1 carbon gen9.
Correct, its usefulness depends on software working as expected (and not being tampered with)
echo 1 | sudo tee /sys/devices/platform/thinkpad_acpi/leds/platform\:\:micmute/brightness