I have PMUnimix installed, you can see it on my screenshots

What I remember now:
As I wrote in my comments before, for Linux Mint Cinnamon 22.1. the 6.11.xxx OEM kernel solved the problem with the Sound, there was exactly the same problem: sound poor, because of MONO. OEM Kernel changed it to STEREO.
I guess it is much to much work to forge an UNIAUD from that OEM Kernel version, and in addition that MAY only help for this specific hardware, I have.
I will try PMUnimix settings this evening.
Thanks again and all the best!!