Notice - To use Audacity on your macOS, always to make sure the USB-Audio-Grabber is plugged on your mac's USB port, and Audacity software is not open.
Step 2 -Open Audacity & make necessary Settings.
Make sure your hardware is fine, then we need to configurate the Audacity before using it recording audio. Click "Audacity" ---> "Preference"
2 - 1 Devices settings
Select "Devices" and make proper settings for "Playback" & "Recording / Device:". Here USB PnP Audio Device is the correct setting.
2 -2 Recording settings
At Recording please do choose "Software Playthrough of input", otherwise you can not hear the audio while recording.
3 - Start Recording
After the correct settings, you can find MIC Source, Stereo Recording, Built-in Output are well selected.
Now we just click the Red Record button ( )to start audio recording.