I just want to shut down the annoying led of my S/PDIFF port... and this is how I managed to do it:

sudo amixer set 'IEC958',16 off

Now, how to configure it forever?

That's another story.

why does amixer need sudo and alsamixer doesn't?

EDIT: I wasn't choosing the card: -c 0 does not need sudo.

Good.

Made a shepherd one-shot service for this lol
it worked!

Oh no! it doesn't work on reboot I guess because this is launched before pipewire!

I have no idea on how to configure this IN pipewire, so I think I need to just make a service dependency here and hope for the best.