I'm using Fedora 34 which ships with PipeWire in full PulseAudio compatibility mode. My Lenovo ThinkPad X1 Yoga laptop exposes two recording devices: one for the built-in microphone array, and one for the line in/headphone jack. 

The headphone jack device is inactive until and unless a headphone device is plugged in. The applet therefore does not show it at all, and the KCM only shows it if you click Show Inactive Devices"

However, this inactive headphone jack device was selected as the default microphone. As a result, the first time I tried to record audio, it did not work, and the applet was no help because it was not actually showing the inactive device that was incorrectly selected as the default!

I had to go into the KCM, show inactive devices, and then figure out that the inactive microphone device was being used as the default one. Picking the active device to be the default input fixed everything, and now that setting is persistent, so all is fine.

However, it was still a problem that the initial default device was set to an inactive device.

Possible an upstream issue, but I thought I'd report this here first just in case it's our fault somehow.