The mic mute led of my ThinkPad X1 Carbon Gen 9 doesn't work anymore after updating linux to version 6.
I can still turn it on by running
echo 1 > /sys/class/leds/platform::micmute/brightness
With linux-lts it still works fine.
This is caused by a behavior change of the kernel code controlling the LED to only turn on the LED when all inputs, including e.g. the jack mic input are turned off in the alsa-mixer settings.
But most userspace code only turns the mic which it is actually using on/off when you hit the mic-mute hotkey.
Also see: https://bugzilla.redhat.com/show_bug.cgi?id=2134824
Which is the same bug.
There is a set of fixes available in the form of an alsa-ucm update which tells the kernel to ignore the state of the jack mic input restoring the old behavior:
The easy way is to ask your distro to update the UCM configuration to the recent one.
Note that all previous kernels have a bug which may cause that the microphone LED is not updated correctly with the sof-hda-dsp driver. Just plug something to the analog jack on your system and mute/unmute/mute the analog input. The microphone LED will follow those changes, too. So you cannot trust the state for the old kernels anyway.