SDDM greeter black screen after upgrade to Kubuntu 25.10

SDDM greeter always gives No Signal after upgrading from 25.04 to 25.10

At first, I think it's nvidia driver issue. So, I changed these files below:

1. /ets/default/grub

   GRUB_CMDLINE_LINUX_DEFAULT="quiet nvidia_drm.modeset=1 nvidia_drm.fb_dev=1 resume=UUID=3fd0f470-9846-4bf7-a286-390f9c99b275"

2. /etc/modprobe.d/nvidia-graphics-drivers-kms.conf

   options nvidia_drm modeset=1
   options nvidia_drm fbdev=1

   both number 1 and 2, cause I think it was nvida driver 580 has problem with wayland

3. /etc/modprobe.d/blacklist.conf

   blacklist nouveau
   options nouveau modeset=0

   cause I thought the nouveau driver also runs when nvidia driver is already running.

   NOTE: After number 3, I ran

   sudo update-initramfs -u
   sudo update-grub

Nothing works. The SDDM still gave me No Signal

Then I found strange things, I typed my password during black screen then I was able to go into desktop.

Turns out, SDDM greeter runs on X11 and I don't have xorg installed. The steps are as follows,

1. Install xorg

   sudo apt install xorg -y

2. Populate /etc/X11/xorg.conf with nvidia-xconfig

   sudo nvidia-xconfig

Just like that, and the greeter was able to display on the next reboot.

Welp, it's weird because previously on Kubuntu 25.04 everything went well. Perhaps during upgrade process via do-release-upgrade, somehow xorg was uninstalled

UPDATE

It's indeed that xorg was removed by 25.10. But it's said that it's only for gnome, and even though I use KDE it's still got removed.