Comment 71 for bug 1834771

Thanks Uriel Tunn, but that fix didn't work for me.

So, I followed your advice and tried an upgrande to another distro.
I tried...
-> Linux Mint 20.2 Uma (Kernel 5.11)
-> MX Linux 19.4.1
-> Manjaro xfce 21.0.7-210614 (Kernel 5.10)
-> Endeavour-2021.04.17 (Kernel 5.11)
-> Pop_OS_21.04_amd64
-> Fedora_Workstation_Live_x86_64_34-1.2
-> Ubuntu 21.04 desktop amd64 (Kernel 5.11)
-> Ubuntu 18.04 desktop amd64 (Kernel 5.4.0-42-generic)

None of the above work with a DVI/HDMI or Display Port/HDMI adapter.

HOWEVER, seeing as i had just installed Ubuntu 18.04, I started to install some kernels on that build

Sure as hell....
4.15.0-041500-generic - work perfectly, DVI/HDMI or Display Port/HDMI adapter listed as an options in Sound Settings
4.18.0-041800-generic - work perfectly, DVI/HDMI or Display Port/HDMI adapter listed as an options in Sound Settings
4.18.10-041810-generic - work perfectly, DVI/HDMI or Display Port/HDMI adapter listed as an options in Sound Settings
4.18.16-041816-generic - work perfectly, DVI/HDMI or Display Port/HDMI adapter listed as an options in Sound Settings
4.18.19-041819-generic - work perfectly, DVI/HDMI or Display Port/HDMI adapter listed as an options in Sound Settings

THEN
4.18.20-041820-generic - would not even boot with Ubuntu - had to use the recovery kernel option, and when i got into the main screen, i checked the sound settings, and sure as hell neither DVI/HMDI nor Display Port/HDMI were listed anymore!

Next I checked
4.19.0-041900-generic - while this didn't give any problems booting, when i got into the main screen, i checked the sound settings, neither DVI/HMDI nor Display Port/HDMI were listed anymore.

So, yes, whatever happened in 4.18.20-041820 has broke the sound for my HDMI adapters and never been fixed since.