The built-in speakers of this laptop was working perfectly and when I tried to connect the external speakers to its headphone jack, there was a big silence in the room.

After the RTFM, I’ve found the following command:

$ mixerctl -av

Which has displayed a very interesting variable:

outputs.hp.mute=on

Hmm, so that one mutes the “HP” output somehow, suggests the name. Let me see if I can get the magic smoke out of this ~12 years old laptop:

$ mixerctl outputs.hp.mute=off

That’s it, now it’s working but I think(read, believe) it’s just temporary and if I restart(or even logout?) it will disappear. Later I’ll update this post and share the result of writing this variable into the /etc/mixerctl.conf.

Update

It’s working like a charm. No need to run mixerctl after each and every reboot.