I updated my Kubuntu laptop to 25.10 directly from 24.04, mostly because I was having multiple display issues and was hoping Wayland would be better. It was in most ways, but this old problem returned:
On the SDDM login screen with an external monitor connected, the secondary monitor login desktop is duplicated on top of the main screen login and displays also on the secondary monitor. This is not an uncommon issue apparently and there are many posts on various ways to fix it. However all of them involve editing the Xsetup file for sddm and none of them work.
Lenovo Yoga 730 laptop, circa 2018, dual video cards - nvidia+intel.
One of the important variables (I think) is the fact that the laptop screen is 4K and the external monitor is 1080p. Note that the overlapping window is 1/4 size of the laptop monitor. This might explain why my desktop does not exhibit the same behavior - it's screens are both 4K.
Oddly, my desktop does not do this with dual monitors. I tried in vain for many hours to get the login screen to appear on only one monitor on the desktop PC but that never worked either.
Everything I have read says SDDM is using X11 and the Xsetup file is used, but it seems obvious it's being ignored.
So you can see what I'm describing - here's is a pic of the laptop login screen when the external monitor is connected:
The upper left is an "active" duplication of the second monitor. By active I mean when I scroll the mouse over the the let monitor, the mouse cursor also shows in the overlaid window. You can see the mouse cursor in the image.
On the SDDM login screen with an external monitor connected, the secondary monitor login desktop is duplicated on top of the main screen login and displays also on the secondary monitor. This is not an uncommon issue apparently and there are many posts on various ways to fix it. However all of them involve editing the Xsetup file for sddm and none of them work.
Lenovo Yoga 730 laptop, circa 2018, dual video cards - nvidia+intel.
One of the important variables (I think) is the fact that the laptop screen is 4K and the external monitor is 1080p. Note that the overlapping window is 1/4 size of the laptop monitor. This might explain why my desktop does not exhibit the same behavior - it's screens are both 4K.
Oddly, my desktop does not do this with dual monitors. I tried in vain for many hours to get the login screen to appear on only one monitor on the desktop PC but that never worked either.
Everything I have read says SDDM is using X11 and the Xsetup file is used, but it seems obvious it's being ignored.
So you can see what I'm describing - here's is a pic of the laptop login screen when the external monitor is connected:
The upper left is an "active" duplication of the second monitor. By active I mean when I scroll the mouse over the the let monitor, the mouse cursor also shows in the overlaid window. You can see the mouse cursor in the image.