[phyrrus9]

I haven't done much in the way of NVMe drives in a grub installation, but they might not be supported in the current production release. The grub-git AUR package (if you're on Arch) apparently has patches for this, but you might want to wait until it's stable.

Source: https://bbs.archlinux.org/viewtopic.php?id=209653

They are. Sometime around the dawn of linux-4 they got official support (way before samsung monopolized on them). Unfortunately I'm not running arch (although the package would still work).