Of course I found this closely related question. However, nothing there works with this modern Fedora installation.
uname -a
says it's "Linux 6.4.15-200.fc38.x86_64".
If it matters, here are the pipewire packages installed:
pipewire-0.3.71-2.fc38.x86_64
pipewire-libs-0.3.71-2.fc38.x86_64
pipewire-pulseaudio-0.3.71-2.fc38.x86_64
pipewire-gstreamer-0.3.71-2.fc38.x86_64
pipewire-alsa-0.3.71-2.fc38.x86_64
pipewire-jack-audio-connection-kit-0.3.71-2.fc38.x86_64
pipewire-utils-0.3.71-2.fc38.x86_64
From this - that it includes both pulseaudio and alsa - I'd imagine it already has the correct software on it, but nothing I've tried works.
For a good description of what just doesn't work at all, please see the afore cited link. However, I've additionally tried quite a few things...
Perhaps most promissing was this:
$ pactl set-sink-volume 0 -5%
Connection failure: Connection refused
pa_context_connect() failed: Connection refused
I think that's promising because it says it's refused NOT that there's no server, "host is down", or that kind of thing. However, as it does this with both user accounts and root, suggests I'm wrong to think that's promising!
I'll gladly try specific things and post results, but I didn't feel it was useful here to do so without being asked.