Comment # 10 on bug 1191247 from Takashi Iwai

(In reply to Andrea P from comment #9)
> > OK, then to make things easier:
> > - Try to boot with a boot option "3"
> >   This will boot to Linux console without GUI
> > - Login there, plug USB-audio device, test directly via aplay
> >     % aplay -Dplughw:XXX foo.wav
> >   as mentioned in the above.
> > - Do suspend/resume
> >     % systemctl suspend
> > - Check again aplay and confirm the mono output
> > - Unload / reload the module
> >     % sudo modprobe -r snd-usb-audio
> >     % sudo modprobe snd-usb-audio
> > - Test aplay again
> 
> done, I can confirm it sound in mono. Once I try to reboot the usb module,
> it gives me "Device or resource busy". Please see screenshot attached
> "rebooting usb module".
> Thanks!

Unloading the module is with modprobe -r, not with -f.
But I guess pulseaudio or pipewire is running even on Linux console, which 
would blocks the operation in anyway.  Hm.

Maybe you can login as root and test in the same way.  If it still gives a
resource busy error, try to run like:
  fuser -k /dev/snd/*
then run the command (aplay or modprobe).