UPDATE: After upgrade to Debian testing (trixie/sid): plasmoids still don't work, KDE doesn't find sound devices.

[René J.V. Bertin]

On Wednesday September 20 2023 13:12:02 A. F. Cano wrote:
>ps -aux shows pipewire is running.  Kmix, that I had to install as it
>didn't come installed by default, only shows the dummy output device.

On my system I often have to restart KMix after restarting the PA daemon, but that's mostly  to get the volume control buttons to work again. KDE uses Phonon for audio output, preferably with the Phonon VLC backend. This used to give you a choice out of all detected audio devices plus the pulseaudio (PA) daemon, in the version I have installed nowadays it has to be PA. IIRC there is a compatibility layer in PipeWire that makes it visible to applications that only support PA; you'll probably want to install that. If you have already and it still doesn't work ... I'm out of ideas.