On Motorola Moto ONE Vision, Android 10, QSAS18.104.22.168:
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.