I am trying to install Ubuntu onto a bootable external hard drive, usb 3.0, but during the final stages of installation where one chooses the device for boot-loader installation the device does not appear. This is being performed on a Dell Alienware R4 and it is booting from legacy mode with nomodeset turned on (as I get a black screen with a mouse cursor otherwise).
The only options presented under device for boot-loader installation are to install onto my internal C and D drives and does not show an option for the external, yet the drive appears in Disks as a cdrom. I have even tried switching usb ports to no avail.
Here is the external that I am using, and below are the configurations made in Rufus: