Comment # 9 on bug 1207129 from Takashi Iwai

It seems that some of weird behavior of the volume up/down is caused when
pvucontrol is opened at the same time.  My understanding is that pavucontrol
tires to keep the shown volume there, and it drags the actual volume while the
apparent volume has been already changed by the up/down key event.

Other than the volume job issue, it seemed working on my machine.  But my
system is with the updated version of pipewire, and that might be difference. 
(And DE is XFCE.)
You can find the update packages in OBS home:tiwai:leap-15.4:update repo.

The non-working mic on your machine is a bigger problem, though.  If it's
reproducible, please make sure that you didn't (mic-)mute it.  There is a
hardware mic-mute function, and this isn't notified to the OS.

Also, you can try to record directly like:
  % arecord -Dplughw:1 -fdat -vv foo.wav
where "1" is the card number of this device (see /proc/asound/cards).

If you get a busy error, try to stop pipewire temporarily:

  % systemctl --user stop wireplumber
  % arecord ...
  % systemctl --user start wireplumber