External Screen Problem (with grub and lightDM)

I have an old screen using VGA cable. I use it as my external screen for my laptop using a HDMI-VGA adapter. But when I power my machine, GRUB and LIGHTDM use my external screen instead of my laptop screen. How can I use my laptop screen on grub and lightDM?
Sorry for my bad English.
Merci d'avance!

Photo: grub and lightDM


Xin Chao.
grub use only the primary monitor and only one.
Don't know about lightdm.
je suis desole.

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Do you know how can I set laptop monitor as primary monitor instead of the external screen?

Right now (at this moment) I can recall only setting primary at the OS, not at grub. I'll come back to you if I can remember or if there is really a way. If others can help, it will be good.
Again, sorry, I have no answer right now.

ps: but I think it has to be done at the hardware side.
ps: for me, the grub and bios screen is always at the laptop.

I really appreciate it.
I have already set primary monitor in settings and it was not effective. I also looked over the BIOS but nothing there seems useful.

For the BIOS screen, there is no software solution. Only if BIOS had an option. VGA is always preferred.
For LightDM it follows Xorg configuration, but you may also use an Xsetup script. Check lightdm.conf for possible settings.
Archwiki has more.

Sounds useful, I'll give it a try.
Thank you!

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