You have an error in the grub configuration saying what device to write the bootloader to. "/" is never a valid answer for this, so it's unclear why this would ever have been in your configuration.
You will need to run `sudo dpkg-reconfigure grub-efi-amd64-signed` to point to the correct EFI System Partition for your system.
You have an error in the grub configuration saying what device to write the bootloader to. "/" is never a valid answer for this, so it's unclear why this would ever have been in your configuration.
You will need to run `sudo dpkg-reconfigure grub-efi- amd64-signed` to point to the correct EFI System Partition for your system.