The strange thing is that the system sound settings or pavucontrol (Pulse Audio Control Center) show microphone activity correctly in the little red indicator bar. However the microphone only records static.
Not so strange at all. I think the problem is usually either a miswired mic (see the other thread on this topic) or a disconnected or broken wire. None of these things would be automatically detected by software.
@Brad: My Librem was out of warranty, and the impression I got from support is that it’s complicated enough to diagnose and repair that they didn’t want to guide a customer through a home repair. I decided I could live with a nonfunctional internal mic.