Pour gèrer la configuration de ses écrans sous KDE, 2 outils existent

kscreen-console --help

Utilisation : kscreen-console [options] bug|config|outputs|monitor|json [args...]
KScreen Console is a CLI tool to query KScreen status

Commands:
  bug             Show information needed for a bug report
  config          Show KScreen config files
  outputs         Show output information
  monitor         Monitor for changes
  json            Show current KScreen config

Options :
  -h, --help  Displays help on commandline options.
  --help-all  Displays help including Qt specific options.

Arguments :
  command     Command to execute
  [args...]   Arguments for the specified command

kscreen-doctor --help

Utilisation : kscreen-doctor [options] [output.<name>.<setting> output.<name>.setting [...]]
kscreen-doctor allows to change the screen setup from the command-line.

Setting the output configuration is done in an atomic fashion, all settings
are applied in a single command.
kscreen-doctor can be used to enable and disable outputs, to position screens,
change resolution (mode setting), etc.. You should put all your options into 
a single invocation of kscreen-doctor, so they can all be applied at once.

Usage examples:

   Show output information:
   $ kscreen-doctor -o
   Output: 1 eDP-1 enabled connected Panel Modes: Modes: 1:800x600@60 [...] Geometry: 0,0 1280x800
   Output: 70 HDMI-2 enabled connected  HDMI Modes: 1:800x600@60 [...] Geometry: 1280,0 1920x1080

   Disable the hdmi output, enable the laptop panel and set it to a specific mode
   $ kscreen-doctor output.HDMI-2.disable output.eDP-1.mode.1 output.eDP-1.enable

   Position the hdmi monitor on the right of the laptop panel
   $ kscreen-doctor output.HDMI-2.position.1280,0 output.eDP-1.position.0,0

   Set resolution mode
   $ kscreen-doctor output.HDMI-2.mode.1920x1080@60 

   Set scale (note: fractional scaling is only supported on wayland)
   $ kscreen-doctor output.HDMI-2.scale.2 

   Set rotation (possible values: none, left, right, inverted)
   $ kscreen-doctor output.HDMI-2.rotation.left 


Options :
  -h, --help                   Displays help on commandline options.
  --help-all                   Displays help including Qt specific options.
  -i, --info                   Show runtime information: backends, logging,
                               etc.
  -j, --json                   Show configuration in JSON format
  -o, --outputs                Show outputs
  -d, --dpms <off>             Display power management (wayland only)
  -l, --log <comment>          Write a comment to the log file
  --dpms-excluded <connector>  Do not apply the dpms change to the output with
                               said model names

Arguments :
  config                       Specific output settings are separated by
                               spaces, each setting is in the form of
                               output.<name>.<setting>[.<value>]
                               For example:
                               $ kscreen-doctor output.HDMI-2.enable \ 
                                              output.eDP-1.mode.4 \ 
                                              output.eDP-1.position.1280,0
                               Multiple settings are passed in order to have
                               kscreen-doctor apply these settings in one go.