Hey folks - found this thread while dealing with this issue for the last several weeks.
It would appear some combination of Realtek driver updates and Windows updates creates this. I got a brand new laptop from work (Dell XPS) and mic on my Q35 Bose Headphones worked fine until all of the updates processed throughout the following 2 weeks after getting the laptop set up.
I can't do a lot of the steps in this thread without full admin permissions, so I decided to try the most logical first before bugging our IT person to help. I went to Dell's website and looked up the drivers for this laptop. There was a recommended driver for Realtek Audio. I downloaded that and installed it. This required removing the old drivers, restarting, installing the new drivers, and restarting one more time. When everything came back the headset was recognized and mic is working fine.
That was all I did, no messing around in device manager or deleting devices.
The only other thing I did was the step Amy mentioned a while ago at the beginning of this thread (checkbox in the more settings for Bluetooth). That didn't seem to change anything though, only getting those new drivers and replacing the other ones.