But when booting official release without HDR patches/advanced, I can choose my HDMI display and blank the laptop panel.
Standard Generic builds are very different, they use X11 windowing system. HDR-enabled builds don't use that. I suppose something needs to be fixed in Kodi in order to enable output to an external display on your laptop.
There is no Prime DRM option to activate on Kodi Player windows config...
DRM PRIME is a Linux thing.
HDR will not work in Windows on GLK. No HDR support in Windows driver AFAIK.