Bug 513416

SUMMARY
When the PC is left unattended, the screensaver automatically shows and the the screens normally shut down. In this case, the screen remained on during 3 mins with a low luminosity.
This does not occur every time.

STEPS TO REPRODUCE
1. Don't the PC until the screens shut down (after showing screen saver)

OBSERVED RESULT
The screens are frozen with a very low luminosity.
Virtual terminal (Ctrl+Alt+F1) does not show, the only way to recover was to hard reboot the PC (by holding the power button)
After reboot, journalctl -b -1 shows the following messages (the ones from `kwin_wayland` are shown in yellow):
```
déc. 15 20:12:26 systemd[1]: Started dbus-:1.2-org.kde.powerdevil.backlighthelper@3.service.
déc. 15 20:12:27 kernel: Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7
déc. 15 20:12:27 kernel: Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7
déc. 15 20:12:27 kernel: Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7
déc. 15 20:12:27 kernel: Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7
déc. 15 20:12:27 kernel: Lockdown: systemd-logind: hibernation is restricted; see man kernel_lockdown.7
déc. 15 20:12:36 systemd[1]: dbus-:1.2-org.kde.powerdevil.backlighthelper@3.service: Deactivated successfully.
déc. 15 20:13:27 kwin_wayland[2760]: atomic commit failed: Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
déc. 15 20:15:04 kwin_wayland[2760]: Setting dpms mode failed!
déc. 15 20:15:04 kwin_wayland[2760]: Atomic modeset test failed! Argument invalide
```
The last two lines being repeated thousands of times (literaly)

EXPECTED RESULT
The screen should show the login prompt and the virtual terminal should be accressible

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20251211
Kernel Version: 6.18.0-2-default (64-bit)
KDE Plasma Version: 6.5.4
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1
Graphics Platform: Wayland
Processors: 16 × 11th Gen Intel® Core™ i7-11800H @ 2.30GHz
Memory: 16 Gio of RAM (15.4 Gio usable)
Graphics Processor: llvmpipe
External monitor: Acer Technologies S271HL

ADDITIONAL INFORMATION
Let me know if any further information is needed.