I have a Mac (El Capitan OS X 10.11.6) and Audacity 2.3.3.
My new Fifine K668 mike is recognised by the Mac and I’ve used it in iMovie.
But I can’t get Audacity to recognise it.
Is it a USB mic?
Ensure that the mic is connected before launching Audacity. It should then be available in the Device Toolbar.