Comment 17 for bug 1705369

Thanks again.

It's starting to sound like your 'nomodeset' fix works because you've still got a modesetting GPU enabled (the Intel GPU). As such, I expect that's the only GPU that Wayland will find by default. But if your monitor is plugged into the Nvidia card then Wayland is displaying to an unused card/connector. So as far as GDM is concerned it has booted on a machine with an Intel GPU and no monitor connected, hence the black screen. That's my theory anyway.