I have a Dell XPS 15 9570 running Windows 10.
I purchased an external Dell Thunderbolt 3 drive to enable me to boot Ubuntu without touching the Windows 10 install on the internal SSD.
I have configured the BIOS to allow booting from Thunderbolt 3 using the instructions here:
I have a USB key with the Ubuntu 18.04.1 installer.
I successfully booted from the USB key.
I can see the Thunderbolt 3 drive from the installer and the installation appears to complete successfully.
When I reboot, I can see the Thunderbolt 3 drive in the boot sequence in the Bios Boot options.
When I attempt to boot from the the Thunderbolt 3 drive a message pops up too quickly for me to read and the machine restarts.
Anyone got any experience of a similar setup?