Dual monitor setup @ login

[fg-personal]

I am a neophyte, I have just installed Debian 12 and I have a dual monitor setup. As I get to the login manager of Debian 12 I can only see the login manager on the laptop screen and nothing appears on my external monitor. That's obviously not what I want, I set the external monitor as primary in the KDE desktop manager for this reason.
Although I understand the login manager and the desktop manager are 2 different things, that's definitely something that can bug a neophyte coming from Windows.
Ideally, I would also like to have the GRUB screen appearing on my external monitor, and not only on my laptop screen, but that's maybe a bit more complex?

I suppose this situation could be somewhat general and maybe it's something that can be easily included in the script. I am not aware of dual monitor issues, but if there were more, a folder with dedicated scripts could be useful, idk.