in configuration.nix for disk-config.nix
boot.loader.grub.enable = true;
boot.loader.grub.efiSupport = true;
boot.loader.grub.mirroredBoots = [
{ devices = [ "nodev" ]; path = "/boot"; efiSysMountPoint = "/boot"; }
{ devices = [ "nodev" ]; path = "/boot2"; efiSysMountPoint = "/boot2"; }
];