Gnome Display Manager (GDM) - Ubuntu - Primary Monitor

[waewoo]

Hello,

I'm desperately trying to configure the GDM (Gnome Display Manager) to display the login page on the monitor attached to my dock (via DisplayLink) (and not on my laptop). :(

To do so, I followed the following procedure:
a) Configuration of my external monitor (attached to my dock) to be my primary monitor with the tool "gnome-control-center display".
b) Application of the following procedure for my GDM to use this configuration
https://wiki.archlinux.org/index.php/GDM#Setup_default_monitor_settings

Unfortunately, this does not work. :confused:

On the other hand, this procedure works well when my external screen is connected live on my laptop.

So it seems that there is a problem or something that needs to be done to make it work when my external monitor is connected to my dock.

For information :
- I use a wavlink wl-ug39dk1 "dock".
- My OS is ubuntu 20.04
- My screen is a HP 32 inches

I've attached my xml configuration file if it helps.

If someone has a solution to solve this problem, it would be great ! :)

Thanks