I just tried installing Ubuntu Budgie spin on a USB and it seemingly deleted/replaced my Linux Mint bootloader from an internal drive so I could no longer boot Mint without plugging in the Ubuntu USB. When I tried to boot from the Mint drive I just got a blank Grub prompt instead of a list of kernels.
Thankfully I was able to reverse this using Timeshift.
How do you avoid this? I didn’t see any relevant options in the Live USB install process. And I have had similar problems like this before.
The behavior I want is to have two standalone Linux bootloaders on separate drives. I suppose I could just disconnect all system drives during install so that the Ubuntu install process can’t fuck with it…
I think there’s a way to make persistent changes to a USB environment, but admittedly I am not sure.
Sorry I can’t be of help here, but at least I can tell you the original approach is meant for regular installs, not installing on a remote USB.