[Soli]

As I said, the Windows desktop isn't color managed. But apparently MS have done some crude (and non correct) form of tone/gamut mapping of the desktop/SDR when enabling HDR. I read the new insider version includes new options to tailor this to your liking. Along with general color management, when you put SDR in a HDR container you should let the user customize the brightness of the SDR (brightness as in luminance, not as in black level) part. Maybe MS has added these options in the new Insider build, but they have probably f***** up once again. They'll get there eventually...

Btw the problems with wrong colors on the desktop (and non color managed apps) is also a known problem for photographers with Adobe RGB monitors. In this case the colors would bee too saturated. Apple has had proper color management since 1993, even iOS is properly color managed since iOS 9. So when Apple finally decides to support HDR you can bet they won't f up like MS...but I digress.

I've answered your main question a few times already. When in exclusive mode, madVR should be able to autoswitch to HDR. I set this up on my friends TV with LG B6 OLED, along with calibrating it. I've told him not to touch anything. But I don't think it even matters to him since there isn't any proper HDR content yet. There might be a specific driver/kodi/madvr/setting combination, but if it was then can't remember. Anyways I believe there will be improvements in madVR regarding compatibility (to HDR autoswitching) in the coming months.