we have 'dim screen totally' and 'dim screen half' and the shortcut to go to systemsettings > energy saving.
In the keyboard-shortcuts we can define a key-combination to 'turn monitor off'

Wouldn't it be a good idea to have this feature exposed in krunner?
And, i would propse to simultaneously start the 'lock screen' as well, so keyboard inputs on the completely black screen don't do sth. bad in the meantime