grub-install ✔
Installing for x86_64-efi platform.
grub-install: warning: disk does not exist, so falling back to partition device /dev/nvme0n1p2.
grub-install: warning: disk does not exist, so falling back to partition device /dev/nvme0n1p2.
grub-install: warning: disk does not exist, so falling back to partition device /dev/nvme0n1p2.
grub-install: error: disk `hostdisk//dev/nvme0n1p2' not found.
grub-install is normally invoked with the target device. “set boot=(hd0,gpt6)” suggests that is /dev/sda, but you might have to use --efi-directory and --boot-directory if grub-install doesn’t work out the right places. I’d use -v too, to get it to tell you what it’s doing.