How to test microphone hardware on my iMac

Ensure the in-built microphone is selected as the system audio input in System Settings, and by removing any external audio that’s plugged into the iMac, then usually testing with a built-in app that uses the microphone.

If that fails, check the microphone again while booted in Safe Mode.

Then contact Apple Support. Use the Support link in the lower left corner of this webpage and chat or call.

Here’s a longer write-up of some options:

… https://www.howtogeek.com/682514/microphone-not-working-on-a-mac-heres-how-to-fix-it/

create a photobooth video.

Create a voice memo.