audio: microphone input volume problem in video calls

On Motorola Moto ONE Vision, Android 10, QSAS30.62.24.3:

My voice is barely audible to the people I'm talking to, on WhatsApp and instagram videocalling. Dust or anything blocking the microphone's audio input was checked, but everything was fine. I even tried to connect an external microphone (videomic mounted), and my voice volume was still low for my interlocutor.

When I shoot a video in the built-in camera app, there is no problem with audio recording. The same happens when sending audio messages from WhatsApp and instagram, everything is fine then.

I suppose it must be something to do with simultaneous audio input / output, or maybe the microphone noise reduction software, but I can't find where to adjust it.