Windows 10 October (1809) HDR Update
Apparently, the latest major update would 'fix' HDR in Windows 10.
Leaving the controls to Windows (if you have an Nvidia, leave to default color setting) and enabling the HDR toggle would be all that's needed - When viewing SDR content, the output would be set to RGB (4:4:4) 8 bit (dithering) HDR Color space and it would switch to 4:2:2 10-12 bit when viewing HDR content (games or videos).
Now, that's what I read from a single user in a forum somewhere but I do wonder if that's true. From my personal experience, the toggle does seems to play nicer with SDR content (displays properly) and Windows does state RGB 8 bit HDR by default under display adapter. The TV (in my case LG C8) is considering the signal as being permanently HDR so no more convenient HDR logo popping up. That being said, no way of knowing if the bit depth changes when going in full screen for a game or movie as I can't have a look at the display adapter read out.
I used to leave the toggle off before (using MPC MADVR LAV for HDR movies) but leaving it off disables HDR in windowed mode (online streaming services) and prevents HDR from working in some games (Shadows of the tomb raider for example). Being 100% certain the toggle works as intended would mean best setting at all time without fiddling with settings, software and drivers.
Any help would be immensely appreciated.