I installed Ubuntu 18.04 on my iMac couple of days ago and it works fine with Nouveau driver.
Additional Drivers tab recognizes the NVIDIA card and suggests to use NVIDIA 340.107.
I installed it but on reboot it gets stuck at NVIDIA logo.
I downloaded and tried to install the .run file by booting into terminal mode (terminal from grub menu, Ctrl+ Alt + F3 terminal option, as well as telinit 3 option).
Using .run file it installs fine if I select NO for DKMS option. But fails if I select YES there.
Using Additional Drivers tab, I see no error. It just asks to reboot.
have spent days already and now at the dead end.
any suggestion is greatly appreciated.