Somewhere between the the last 11.x version of PulseAudio used on the 19 series of Mint, and the 13.99.x version used in Mint 20, something was introduced that affected a not insignificant number of users.
I've tried my best to find the cause or at least a workaround and the very limited success achieved was downgrading PulseAudio to the version in the Ubuntu security repo that helped a very few users.
A couple of present bug reports are still in progress that will hopefully resolve this. See here and here. There may be more, but I stopped looking after finding those two that seem relevant to the issue.
To know if you're affected, the output of
pacmd list-cardsmight show something like this for your built-in sound card:
That is the most common symptom I've seen, and it may have been somewhat intentional based on the dialogue in those bug reports, meaning if nothing is plugged in then maybe that's what it should show, even though that's never been the case in earlier versions of PulseAudio.Profiles:
input:analog-stereo: Analog Stereo Input (sinks: 0, sources: 1, priority: 65, available: no)
output:analog-stereo: Analog Stereo Output (sinks: 1, sources: 0, priority: 6500, available: yes)
output:analog-stereo+input:analog-stereo: Analog Stereo Duplex (sinks: 1, sources: 1, priority: 6565, available: no)
I've been averaging over 40 posts per day for over a week almost exclusively dealing with this and it is starting to wear me down. I was looking forward to Mint 20 (read Ubuntu 20.04) reducing the sound issues people were experiencing with the upgraded versions of PulseAudio, ALSA, linux-firmware, sof driver and kernel, but that has not been the case. While I'm hoping this might be temporary, I am no longer counting on it. Some developers/maintainers (upstream from Mint) have made some really stupid decisions in the past few months, and there's even more new crap coming down the pike, that I am starting to believe Linux audio is going to be going backwards (for some, not all) for the foreseeable future.
I will update this post if a fix or workaround is found. I do not expect that to occur in the next week. With luck, in less than a month this might be fixed.
P.S. I know this post really belongs in the chat section, but felt it would better reach those affected here.