I can now set 'alsa default' as input/output and record from mic so long as I kill jack (sorry, Jill Cheesy)
I don't get why this is.
According to the audacity forum, the issue has been around since 1.3.3, and has affected people running Slack, Fedora, Ubuntu...
It only seems to occur to some people though, so it might be some messed up hardware or setting that we have.
(As I put in the other thread, I've put the Jack murdering after audacity into a little script that's working great and can be called by the audacity icon.
Running a separate command on the side whenever I was starting audacity was getting on my nerves.)