Microphone limited to very low volume after update to Sonoma.

I have a 16 inch MacBook Pro (2021) with the M1 chip. Until recently I was still on Monterey, and my hardware was fully functional. A few days ago, I updated to Sonoma 14.4.1. I now find that my internal microphone is limited to very low volume, so that, for instance:

(a) I can send a voice message via WhatsApp, but the recipient hears my message as a low whisper.

(b) Attempts to use a language learning app with speech recognition online fail, with alerts asking me to speak louder.

I have tried to increase the volume via Systems Settings/Sound/Input, but that make no difference. From an internet search, I see that previous users switching to Sonoma have had problems with the internal microphone. Is there any way I can solve this problem? If not, is this a known issue, and is Apple doing anything to fix it?