AirPods cannot record for Audacity unless Sound->Input setting is kept open

I try to use Audacity to record my voice with AirPods on. Audacity does identify AirPods as an input device so I select it from the mic list. But it cannot get the voice at all and there is no waveform displayed. However, once I explicitly open Mac's setting Sound->Input (just leave the window there), it weirdly works. As soon as I close the setting or even just switch to other setting tabs, my voice gets lost. (By default, in Sound->Input AirPods is selected even when I open it.) Restarting software/computer does not change this behavior.