I'll create another post regarding zoom tomorrow morning.
Now, I launched droidcam from the terminal, and then ran
pacmd load-module module-alsa-source device=hw:Loopback,1,0 source_properties=device.description=droidcam_audio
in a separate terminal. I can select droidcam_audio as my source sound in Zoom. It also appears in pavucontrol.But of course, when I select it, it still doesn't work.