Comment # 9 on bug 1206760 from Takashi Iwai

You can turn off the pipewire by running like
  % systemctl --user stop wireplumber
(and restart by
  % systemctl --user start wireplumber
 too)

But this means that KDE mixer and such application won't work well.

In general, the modern desktops require the sound daemon.  I guess it worked
casually in your case because the primary card was selected to HD-audio.  And
this should still work.

Try to choose HD-audio as the primary device via pavucontrol.  After that (and
a few seconds later), the PCM device for C-Media should be released, and you
may use other applications with it.