As Audacity continues to evolve they regularly rework the menu.   For version 3.6.1 of Audacity, follow these steps to set the default audio recording format to:

Wav format Mono recording at 48000 hz

  1. Start Audacity
  2. Click on Edit / Preferences and select the first item, Audio Settings
  3. Make sure the following highlighted settings match these

4. Turn OFF overdub

When you are ready to export your audio:

5.  Click on File / Export Audio and make sure the highlighted settings match these: