Hi,
I have exactly the same issue, but with different headphones: Xiaomi Airdots. Balance works with no issues on Android, but in Windows 10 sliders are tied together. I tried your suggestions but they don't work. I've also tried some other . For me it looks like for some reason some headphones have worse driver support , some generic drivers are used, that are more universal. There are no special drivers from Xiaomi for that kind of devices and never will be. Everything is on Windows side. Is there any way to fix it?
So far I use "Equalizer APO" to make it work. Pre-amplifier set separately to each channel