The solution to this is to run X11 as root, so it can use VGA arbiter and detect displays on both the NVIDIA and modesetting drivers.
Add this to /etc/X11/Xwrapper.config : needs_root_rights = yes -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to mutter in Ubuntu. https://bugs.launchpad.net/bugs/1716857 Title: gdm3, hybrid nvidia with modeset=1, no external monitors detected Status in gdm3 package in Ubuntu: Confirmed Status in mutter package in Ubuntu: Confirmed Status in gdm3 package in Debian: New Bug description: Context: 17.10 development packages, nvidia binary driver 375, modeset=1 for the nvidia driver. ubuntu desktop (gnome shell), fresh install ThinkPad W520 in Nvidia Optimus bios mode. Nvidia profile. Result: no external monitors are detected. xrandr does not even list them as disconnected (normally it would list five external disconnected monitors) lsmod shows that nvidia driver is loaded and the modesetting is working at some level because there is no tearing on the laptop panel Note: modeset=1 is the only way to get flicker-free graphics on the laptop panel. modeset=1 is not the default setting but it is highly desirable. It works if lightdm is used which is why I have reported this against gdm3 My sessions in this configuration have mostly crashed after a few minutes with a gdm3 fail whale message in syslog but nothing else looks interesting. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1716857/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp