Mic Not Picking Up Audio EXCEPT for "listen to this device"

[soakedsilence]

Alright, I got a good one for you folks here.
I've encountered a problem like no other. Basically, my computer won't pick up audio from my microphone. It's enabled, it's not muted (system or application wise), and it's not being captured by any rouge application.
First thought - broken, right? Wrong.
If I go into settings and hit "listen to this device"
I hear myself perfectly fine through my headset.
I've reinstalled drivers, I've reinstalled Realtek software, and neither seem to have done anything for the problem. Event logs tell me NOTHING of what happened; It seems like a sudden and incomprehensible problem.

 

[Ralston18]

Do other microphones and headsets work on your computer?

Does the microphone and headset work on other computers/devices?

Make and model headset/microphone?

Any adapters or interim connection cables?

Ensure that you have consistent TS, TRS, TRRS with respect to adapters, cables, plugs, and ports.

What standards? E.g.:

https://help.longtailproducts.com/hc/en-us/articles/207970396-Smartphone-Headset-Standards-Apple-iPhone-AHJ-CTIA-OMTP