After upgrade from v.2 to 3: exception: Failed to open mixer for 'alsa': no such mixer control: PCM

There is no solution here: Failed to read mixer for 'alsa': no such mixer control: PCM

Problem is new in Volumio3. Every time the player loads new song.
Dac: AlloBoss
Mixer set to Hardware.

VOLUMIO_BUILD_DATE=“Sun 25 Jun 2023 07:20:58 PM CEST”

Do you hear sound or not?

If you are just referring to the error in the log, this is harmless

Yes, I thought so, but nevertheless unnecessary log entries can be annoying if you need to look into your logs from time to time (e.g. if you want to know if there are read/permission problems with newly added files etc.).