This may need a bit of adjustment for kms users, as vc4 becomes the sound driver which switches to digital audio and has different device names. But I like the names, so I hope it works out.
When using kms, the sink name changes to:
If you run:
$ pacmd 'update-sink-proplist alsa_output.platform-fef00700.hdmi.iec958-stereo device.description="HDMI"'
It does set the description to:
device.description = "HDMI"
However, the Plasma widget does not reflect that setting, it continues to be called:
Digital Output (S/PDIF)
When using fkms, the widget does change to reflect the setting using the bcm2835 sink.
This same behavior occurs with Plasma on both Raspberry Pi OS and Arch.
When using kms
$ pacmd list-sinks
iec958-stereo-output: Digital Output (S/PDIF) (priority 0, latency offset 0 usec, available: unknown)
So I assume this is what the widget uses for a description.
The S/PDIF is the headphone jack, yet the sink is hdmi. The widget only has the S/PDIF output device. Yet my actual audio-out is hdmi, no headphone output. A bit wonky.
With fkms, the widget has both a hdmi and a headphone analog audio-out.
If you manage to get both Headphones and Digitial Output with kms working, the following works:
pacmd 'update-sink-proplist alsa_output.platform-bcm2835_audio.stereo-fallback device.description="Analog"'
pacmd 'update-sink-proplist alsa_output.platform-fef00700.hdmi.iec958-stereo device.description="HDMI"'