[13.2/KDE] screen brightness no longer adjustable

suddenly (probably after some updates) the screen brightness is no longer adjustable via software.
(via the keyboard it works)
this means that corresponding energy saving settings don’t work any longer.
in system settings -> energy management moving the slider for screen brightness has no effect

the bad thing was that the screen stayed black after ging into energy saving mode.

any ideas whta the reason could be and how it could be resolved?

Videocard? Was a kernel update involved?

Maybe - I don’t know.
What can I do?

when I have the battery symbol in the panel can adjust the screen brightness via the slider of that plasmoid. (=left click on the symbol)
with klipper -> system settings -> energy management (or right click on the battery symbol in the panel) it’s still not possible.

I therefore assume there’s a problem with a KDE module.

No could be many things. So tell use what video card you have and what drivers you installed for it and how. Also is this a Optimus based system. Very important to know that.

15: PCI 02.0: 0300 VGA compatible controller (VGA)
  [Created at pci.328]
  Unique ID: _Znp.dqrsGECRMk8
  SysFS ID: /devices/pci0000:00/0000:00:02.0
  SysFS BusID: 0000:00:02.0
  Hardware Class: graphics card
  Model: "Intel Haswell-ULT Integrated Graphics Controller"
  Vendor: pci 0x8086 "Intel Corporation"
  Device: pci 0x0a16 "Haswell-ULT Integrated Graphics Controller"
  SubVendor: pci 0x17aa "Lenovo"
  SubDevice: pci 0x2214 
  Revision: 0x0b
  Driver: "i915"
  Driver Modules: "drm"
  Memory Range: 0xf0000000-0xf03fffff (rw,non-prefetchable)
  Memory Range: 0xe0000000-0xefffffff (ro,non-prefetchable)
  I/O Ports: 0x3000-0x303f (rw)
  IRQ: 58 (103814 events)
  I/O Ports: 0x3c0-0x3df (rw)
  Module Alias: "pci:v00008086d00000A16sv000017AAsd00002214bc03sc00i00"
  Driver Info #0:
    Driver Status: i915 is active
    Driver Activation Cmd: "modprobe i915"
  Config Status: cfg=no, avail=yes, need=no, active=unknown

…all settings where automatically selected during installation

After moving the slider, apply the settings. The brightness doesn’t change at that instance, it changes only after applying the settings.