@simon probably not the answer you are looking for, but the easiest way to work is to get a basic audio interface (like Focusrite etc), and a mic that plugs into its XLR rather than a USB mic. Then, the audio interface connects via USB3 to the mac. There will be dials that let you hear the mic itself, and the computer.

This is all really easy, since it’s made for musicians, not computer people.