OK seems like it’s a problem between Apple and the rest
I installed Manjaro on an usb stick, booted and tried a lot of things but still no sound
So now, I’m gonna stick to the Bluetooth headphones, no problem
Thanks to everyone for the help
Hi Alain, sure it’s much to late but i try to resolve the same problem and i’ve found this site: Intel_iMac - Community Help Wiki. At the moment i can not check it out.
I have since had the same audio issue on my 2011 iMac. The solution I found was to install PulseAudio volume control, and use it to turn on the internal speaker volume everytime I reboot the computer. An easy solution but an extra step, to be sure.