Yes, @txbob, thanks, I can read.
Edit1: @txbob, toned down: From decades of experience: More often than not things work though “not supported”.
Actually it turns out supported 17.10 chokes as well with at least two Canonical snake-pit idiosyncrasies:
#1 took me “just” an hour or two, not calculating the additional installs and configs: With the eGPU off I get to the login. Under the password in the cogwheel switch to “Ubuntu on Xorg”
#2 hang w/ eGPU on “started gnome display manager and dealing with any system changes” still waiting for solution (will start new thread)
It´s “interesting” that there is no official support for the overwhelmingly important Linux MONTHS after release.
Worse, when I wanted to send the bug report it said “It´s not ours. Go bust.”
On the Dell the Ubuntu 18.04 is just a trial, but on the NUC6i7KYK with the Thunderbolt 3 HP Omen Accelerator eGPU I needed a more recent Ubuntu / Kernel for the TB3 eGPU to get recognized. I could have started to compile a new Kernel for Ubuntu 16.04 or try 18.04.
One should think that things get better / easier with technological advances, but when I look at the NUC BIOS it’s intimidating. You never know enough.
So regarding the Kernel supporting Thunderbolt 3, after days of reading up and weighing the merit of the posts I learned that there is sth like Ubuntu LTS or Hardware Enablement Kernels which let me stay on 16.04 with the minimum 4.13 Kernel for TB3 in 16.04.4.
Could have avoided the callow / immature Snappy and Wayland BS, etc. and the step back to 17.10 (Wayland default trap) because 18.04 (Xorg default) is not yet supported for CUDA.
So it was the old story again: Help yourself to get help.
Had to jump through TWO hoops at once. Decided to dig into GRUB AND boot repair.
Always had wondered why some of my Linux installations didn´t show a boot menu and occassionally went on my *ss by stating that timeout = 0 is no longer supported (or so). Go figure.
So as remedy I wanted to edit /etc/default/grub, but as this was not the active system and I couldn´t run update-grub on it afterwards I had to go for /boot/grub/grub.cfg directly. As the installation was ***** up anyway it couldn´t get worse, so I went for it and commented out several IFs around timeout=30.
And voilà, there was it, the boot menu!
Now Advanced Options > Recovery > dpkg Repair.
And wow, it revived the system with the 396.26 driver!