"Dummy Output" OK, we see occasional cases of that.
Websearch using AMD/ATI Device 1637 dummy output ubuntu 20.04" for your sound device gives:
Only suggestion I see is maybe try a later linux kernel. But using a later version kernel not tested by Zorin devs may or may work, but could give you other issues.
EDIT: Did you try this:
pulseaudio -k && sudo alsa force-reload
Also:
I see you have bought Pro. That gives you entitlement to support from Zorin devs. You could try an email to them, but please be patient for any reply as there are only two of them.