Sometimes only the onboard audio devices show up as being available in gnomeusing pulseaudio. Your usb devices for some reason don't show up. This has occured at some very inopportune moments, such as during online teaching.
If that happens, unplug/turn off the USB device, and run
pulseaudio -k && pactl load-module module-detect
then turn on the USB device again.
It should now be found.
