RE: Dell M.2 FAQ regarding AHCI vs RAID ON, Storage Drivers, M.2 Lanes, Performance and more
i had this same problem, and after about 8 fresh installs and a few days i've figured it out. i have the toshiba 512 nvme kxg5.
use rufus to make a bootable usb in UEFI GPT partition
go into bios and select RAID
plug in the usb, boot the laptop hit f12 to get into the boot menu
since it's uefi, it'll show up, boot to the usb
go to install windows, and you won't see your ssd. you'll do the load drivers like before, just make sure that the latest drivers are on a seperate usb drive, not the usb stick you are using to install windows. i did this at first, and even though i was able to find them, they wouldn't load. i'd grab the intel rapid storage drivers and console from your dell page, and extract them, no need to run the exe. pick your appropriate windows and bit type.
doing this will use the intel iastora drivers, that will let your ssd actually be recognized as a ssd and it will show up in the storage console like from your pic above.
if you do get it working, i'd stay away from the big feature windows 10 update, it seems to slow the ssd down some.