Hi!
Maybe try using the kwriteconfig6 command, assuming you’re on Plasma 6? Based on what’s described here: ubuntu - How to disable the 10 minute screen timeout/lock in KDE? - Super User - it might be worth trying a command like the following (on my Fedora KDE 41 system, these settings are in ~/.config/powerdevilrc):
kwriteconfig6 --file ~/.config/powerdevilrc --notify --group AC --group Display --key TurnOffDisplayIdleTimeoutSec 1200
On my system, that command changes the "Turn off screen: " setting under Power Management to 20 minutes.
Hope that at least helps you on the path toward what you’re looking for!