Recently all my audio disappeared in Ubuntu Studio 21.10 with KDE desktop.

It all worked fine until today, and now there is no audio. I installed Kmix and the sound came back, but in the KDE System Settings program it no longer lists any section for Audio, which was there before.

The volume icon had disappeared from the main Panel, but one reappeared after installing Kmix, at which point audio was working again, but just for a short time, as the audio stopped working again after rebooting.

I had tried uninstalling and reinstalling pulseaudio but no change.

I have tried restarting pulseaudio, or using pulseaudio -k to kill it which had worked yesterday when the audio did not come on at bootup, but it had worked okay after that. Today even that does not work.

What can I do to get back the audio? And to have it listed in the System Settings? And to get back the original icon for sound in the Panel that I had before?