We are also experiencing this issue. I have a Lenovo 20T00023US, brand new, just imaged it. We are using the built in Microphone Array. It is stuck at 67 for the volume level, not sure what is freezing it there, but when using the Mic Array with any other
application sound works fine, even when the user is sitting 3 feet away you can still hear them perfectly. However, when using teams it barely registers as a whisper.
Incidentally this laptop and others that are having the issue are on Windows v2004, while I have tested with my laptop which is an ASUS ZenBook running Windows v1909. Will test more on this shortly.
Obviously Teams online will work fine as the Mic is going through the browser and not through the Teams app.