Comment 0 for bug 1958488

Test environment:
1. A desktop or workstation which containing an iGPU.
2. Plug a nvidia graphic card to the system and installing proprietary nvidia driver (470 in my case)
3. Attach a monitor to dGPU and leave iGPU connect to nothing.
(in my test environment, there is the other ethernet card and TBT4 cards)
4. Reboot system.

Based on:
$ cat /lib/udev/rules.d/61-gdm.rules
# disable Wayland on Hi1710 chipsets
ATTR{vendor}=="0x19e5", ATTR{device}=="0x1711", RUN+="/usr/lib/gdm3/gdm-disable-wayland"
# disable Wayland when using the proprietary nvidia driver
DRIVER=="nvidia", RUN+="/usr/lib/gdm3/gdm-disable-wayland"

It will disable wayland by default if proprietary nvidia driver load.
But in some race condition cases, the nvidia probe is later than gnome launches.
Thus, ubuntu-gdm has a fix for Bug#1794280 to add "ExecStartPre=@libexecdir@/gdm-wait-for-drm".

The gdm-wait-for-drm is intend to make sure all drm udev devices enumerated before launching gdm.

It rely on at least one "master-of-seat" graphic card for gdm but it's not rigorous enough.
Since most of graphic cards are own "master-of-seat"[1].

In my case, it detects the iGPU is probed but dGPU.
However, the display is attached to dGPU.

We need to make sure the targeted gpu (connecting to monitor) is probe before launching gdm.

[1] https://www.freedesktop.org/wiki/Software/systemd/multiseat/
/lib/udev/rules.d/71-seat.rules
/lib/udev/rules.d/71-nvidia.rules