I use i3, and when I plug in a monitor, I just figured out the command i need with xrandr and save it as an alias or command. Or I also found out accidentally,

I use i3, and when I plug in a monitor, I just figured out the command i need with xrandr and save it as an alias or command. Or I also found out accidentally, I had to install gnome for some stupid test. But, using gdm as the login manager made automatic monitor detection work under i3? I literally changed nothing. But using gdm to login to my i3 and it works flawlessly. Even turning off monitors moved everything to one automatically.