nixos-hardware/purism/librem/13v3/README.md

Librem comes with Coreboot + SeaBIOS payload. That means EFI boot is not possible. Use fdisk to partition hard drive, and GRUB as a bootloader:

{
  boot.loader.grub = {
    enable = true;
    device = "/dev/sda";
    version = 2;
  };
}