Only Windows can hear my microphone

I started having an issue about two weeks ago where Windows registers and displays microphones correctly, but then seems to "eat" the input from them so that no other programs pick anything up. If I plug a microphone in and go to sound settings, I can see the input meter rise and fall as I'd expect, but only in sound settings and the Nahmic 2 software my motherboard installed. Skype, Discord, Steam, and every other program I've tried can only pick up a bit of noise when I turn the microphone on or off. I've tried using another microphone, using both the case microphone input and the rear panel input, and reinstalling the Realtek audio driver with no luck.

OS: Windows 10
Motherboard: MSI B350
Realtek driver: 6.0.1.8158

First thought. If you don't have "Stereo Mix" set as the default Recording device, set it as default. Many programs use Stereo Mix as the default source.

Thanks for the quick response.

Stereo mix had somehow gotten disabled, but re-enabling it and setting it as the recording device didn't change anything. The original default was "Microphone", and the input bars only move on that even when stereo mix is set as the default. I tried setting other programs to both microphone and stereo mix input with no luck.