I have a fresh install of Debian 11 with KDE plasma desktop. Every thing was fine until I installed the Nvidia display driver. After reboot the first thing I noticed was the SSDM login screen was messed up. The picture and text was much larger that it should be. After logging in the KDE Plasma display had the same problem. The background displayed beautiful but all the text and icons were much too large. I found that any KDE application such and kate had the same problem. Non KDE applications such Guake terminal and Brave browser display fine.

I installed the Gnome and Cinnamon desktops and there displays are fine. By the way the Nvidia driver seems to be working fine and I even uninstalled it but did not fix the problem. The Nvidia driver is back installed now.

I uninstalled the KDE Plasma desktop with these commands:

sudo apt remove kde-plasma-desktop
sudo apt autoclean && sudo apt autoremove

After reboot I found that SDDM had apparently been removed also and I was left with a Debian login prompt. I reinstalled KDE with this command:

sudo apt install kde-plasma-desktop

Now back with the same display problems with SDDM and KDE. Any Ideas? I would like to use KDE but am happy to use Cinnamon but would like to fix SDDM.
Thanks