I am running 20.04 as well (amd64) and am not seeing the same issue.
In audio & video settings, do you see your sound device under “speakers”, if not default?
And if using gnome, go to “Settings” and ensure that “chromium” and “Skype” sound level is set correctly? For some reason, it shows as “chromium” when running the audio test… probably related to it being an electron app.