Bios version 1.04. If I change integrated graphics controller from "auto" to "forces" then I can choose UMA Frame buffer size.
BTW is there any way to know what panel you have? I have the glossy screen and it looks very good to me but I'm not sure if I got the better panel with 300 nits. My config differs slightly from the one you reviewed, I have a 512gb ssd in mine and the glossy screen. I think maybe the battery differs to, I have a 50Wh battery.