I just downloaded audacity. I plugged in my Notepad 8-FX USB into my laptop USB running Windows 10. I then launched audacity. It doesn’t look like it’s showing up under the mic drop down menu–only my laptop mic is there. The mixer is recognized under the speaker drop down. I’m able to plug my headphones into the mixer and hear my self play with direct line, so I know the mixer is not the issue.
You know the mixer analog parts are OK. You should be able to see the mixer in the Windows audio panels. Right click the speaker icon and drill down to the recording panel. There should also be a little sound meter and you should be able to make it kick.
Audacity gets its sound from Windows, not the device.