Apple - Display Mic volume in the menu bar

This app works for me: MuteMyMic. Available in the App Store at that link.

Appears to be free, as well.

It puts an icon in the menubar with a mic input level slider:

Disclaimer: no financial or other ties to the developer of this amazing app which I just found using Google.

Just wanted to share the following app too - https://apps.apple.com/us/app/mutekey/id1509590766?mt=12

1. Good UI.
2. Adds icon in the menu bar.
3. Ability to add keyboard hotkey.
4. Can select among input devices.
5. Free.

Same disclaimer as earlier answer: No financial or any other ties to the developer. Just found the app on the app store and love it.