Did you try this?
You can also try to select different devices/sound cards in the
If I understand you correctly, then you run KDE, you can try the
plasma volume applet in the
system tray, to check the volume on all devices, and switch devices.
Also check "System Settings" -> "Hardware" -> "Multimedia" for audio settings. Try changing devices, could be that one works, but for some reason did not get selected as default.
Another tool to try could be
pavucontrol. I don't think it is included by default in the KDE version, so you will have to install the package.
Lastly, no offence, but did you update everything? I understand that you might prefer to update less frequently, but then a rolling release might not be the most appropriate for you, since they are built around frequent updates (i.e., quickly getting the latest version of every package).
"pulse audio dummy output" seems to be a common problem, might be some working tips in other places. Good luck!