Ubuntu 22.04 and NVidia GM206 : no HDMI sound

Hello,
Recently, I wanted to test my HDMI sound on my graphic screen, and I have none. The sound in the screen is set at 100%. Other than that, I have a fine sound from my motherboard embedded sound card, and from my USB headsets.
From alsamixer, I see that all the devices from the NVIDIA card are labeled S/PDIF, they are all unmuted, and none has available sliders.
I am a senior Linux sysadmin, but I don't really now Alsa, Pulseaudio. I began reading some articles, discovered aplay -L, /proc/asound/, dev/snd, snd-hda-intel, but I am afraid I am not really skilled here.

Can anybody help me ?
Regards
R. Grasso