If anyone is having trouble with Ubuntu 18.04 installing Diablo 3 - this is what fixed it for me. I installed the latest nvidia drivers by following the guide here: https://github.com/lutris/lutris/wiki/Installing-drivers
For completeness this is the steps:
sudo add-apt-repository ppa:graphics-drivers/ppa
sudo apt update
sudo apt install nvidia-driver-418 libnvidia-gl-418 libnvidia-gl-418:i386
Then reboot the system.
