Input microphone not working

My iMac's internal input microphone doesn't work.

This mostly happens when I use Zoom, my current workaround it using my Bluetooth headphones. But when the battery on those die, so does my voice on that call...

All my settings are as per Zoom's setup which makes me think this might be an iMac issue. Is there something I can look at or check for to make sure my iMac is working correctly from an audio point of view?

I got a new hard drive installed in April (1TB Solid State Drive). Not sure if that's worth mentioning.

Thanks in advance. :)