No ALSA "default" output device

Apologies if this exact question has already been asked and answered - several different searches failed to turn it up.

I’m running Ubuntu 20.04.4 LTS, Audacity 3.1.3 installed from Ubuntu’s Software app.

Audacity thinks it’s playing, but there’s no sound. Other applications (e.g. Rhythmbox) are audible.

I do see here and elsewhere that with the ALSA host, Audacity should be set to the “default” output device. The trouble is that Audacity’s device scan does not report the “default” output device. The input device is set to “default” as I suppose it should be.

The output device dropdown is the same whether viewed from the home screen or from Edit → Preferences → Devices:

HDA Intel: ALC892 Digital (hw:0,1)
HDA NVidia: HDMI 0 (hw:1,3)
HDA NVidia: HDMI 1 (hw:1,7)
HDA NVidia: HDMI 2 (hw:1,8)
HDA NVidia: HDMI 3 (hw:1,9)
HDA NVidia: HDMI 4 (hw:1,10)
HDA NVidia: HDMI 5 (hw:1,11)
HDA NVidia: HDMI 6 (hw:1,12)

Not one of these devices produces actual sound output. I believe that if I were able to select “default”, it would work. How can I coax Audacity to present “default” as one of the selections?

Most likely some other app has grabbed the alsa device.
Try shutting down all other apps (including web browser and background media player), then restart Audacity.