External HDD not bootable after install

[Fabby]

Last-ditch effort:

[HowTo] Chroot from or into any Linux distribution

Difficulty: ★★★☆☆ Step 1: Mount your system. This works for both GRUB and EFI systems/installations Okay, the first thing to do is to be root. To do so, open a terminal and type in sudo -i then hit the Enter key. You may then give in your password if prompted. We then need to create a directory where we will mount the target system. In this case, let’s make a directory named “chroot”, by entering mkdir /chroot in the terminal. Time to find where is your system located!! To do so, you may e…

and instead of an update-grub, do:

update-grub --recheck

If that doesn’t solve the issue, I’m all out of bright ideas!