Hi
Does it happen on a network or wifi phone call when using hands free, as that also uses the microphones in the same manner.
If it does then the question I have is ~ have you recently installed any apps that use the microphone since it was working, Signal, Telegram, a music app. etc.
Please check which apps are allowed to use the microphone and disable them all then restart the phone. Then re-enable them one by one and test the mics. This can take some time as it could be a miox of apps that will not release control over the mics.
Also make sure the mics are working first: