change KDE desktop resolution also SDDM manager in case newest NVIDIA Driver using but wrong detected refresh rate.

[Anton]

1) change SDDM display setting by editing config file in command line (remember we are on safe mode no 'X' session loaded)

before beginning we must install some packages :

'xrandr, 'nano' or 'mcedit' editor from mc package

sudo apt install xrandr mc

do detect monitor properties with xrandr

xrandr -q

open then edit SDDM start script

mcedit /usr/share/sddm/scripts/Xsetup

adding detected xrandr static settings and disable auto detect monitor functions:
_mainFn () {
_logLineFn 'BEGIN report';
# _calcDisplaySetListFn;
# _setupDisplaysFn;
# previsiolly checked parameters
xrandr --output HDMI-0 --mode 1920x1080 --rate 60
echo '=====';
echo "${_debugList[*]}";
echo '=====';
echo;
logLineFn '. END report';
}

2) change /user KDE settings in HOME directory

this catalogues contains the monitor properties

~/.local/share/kscreen/
~/.local/share/kscreen/outputs/

there are files having monitor's parameters
include like that text

"mode": {
"refresh": 60,
"size": {
"height": 1080,
"width": 1920
}
},

edit "refresh" parameter etc

my system: kubuntu (ubuntu) 23.04, KDE 5.27.x, Nvidia DRV 530.41.03, kernel 6.2.x