Ubuntu 18.04 fails to boot even in recovery mode (stuck on loading initial ram disk) on ASUS UX433FA

Solved by following this: Ubuntu 18.04.2 boot stuck on purple screen after updates

The issue was due to an intel microcode update, which behaved badly with ASUS laptops. In short, the fix (for now) is to first add dis_ucode_ldr to the kernel command line. Do this by pressing E while on the grub boot menu and find the line which has something like “ro quiet splash”. Add dis_ucode_ldr at the end of the line. This will let you boot.

Once you boot, run

sudo apt install intel-microcode=3.20180312.0~ubuntu18.04.1

This undoes the problematic update in question and will allow you to boot from now on out (without having to modify grub).