Comment 11 for bug 1410618

Ok folks I managed to solve the issue:

First check wihtout umplugging the cable the result of:
sudo hdajacksensetest -a
Then connect the cable and run it again:
sudo hdajacksensetest -a

There should be some difference, with now some pin marked as "(Not connected): present = Yes" while in the other ther first one it should have said "(Not connected): present = Yes". If this is not the case your cable is not being detected and you may have other issue.

Then run: cat /proc/asound/card*/codec* | grep Codec
And make sure it is Cirrus Logic CS4208, if that is the case, search the particular model of your computer here: https://www.kernel.org/doc/html/latest/sound/hd-audio/models.html (in the CS4208 section if that is your case) find the code of your computer: mbp55 or imac27 or imac27_122 and then edit /etc/modprobe.d/alsa-base.conf
Erase every line in there and write (supposing your model was mbp55:
options snd-hda-intel model=mbp55
Then restart the computer and it should work
(Solution by Doug White)