I’m running ubuntu 18.04 with 4.15.0-20-generic kernel on the same laptop as in this thread: https://devtalk.nvidia.com/default/topic/1033027/
I have tried installing 390 and 396 drivers through apt as well as manual install. In each case I can’t boot with runlevel 5 - it ends with black screen. If I’m booting with runlevel 3 and then starting X’s or gdm3 after login it ends with hanged terminal. All of these steps I can only perform under “nomodeset” because in opposite case black screen appears even before terminal prompt. I did signed installer’s generated keys for secure boot and enrolled it properly so the driver module is loaded correctly and I can see ASCII table by running nvidia-smi.
Here is the bugreport log: https://1drv.ms/u/s!Ar90OrCeEGhtqn5clvvJNIJ9NIwm
Please note that it contains logs for previous installs and uninstalls, so better to read it bottom-up.