Bug 495055

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SUMMARY
As the title says, I'm experiencing a regression for 6.2 where my main monitor fails to stay in standby mode after the time specified in Power Management. Meanwhile, my second monitor enters power-saving mode correctly. This was not an issue under 5.27, 6.0, or 6.1, and has only appeared in the 6.2 series (up to 6.2.1 as of writing). Primary monitor is connected via DisplayPort 1.4, second monitor via HDMI.

STEPS TO REPRODUCE
1. Set the 'turn off screen' value in the Power Management settings section. Optionally, set the 'when locked' option as well.
2. Idle computer until specified time.
3. Observe power-off/standby behavior for monitor(s).

OBSERVED RESULT
Second monitor powers off correctly; main monitor notifies user about loss of signal, then blanks for a short interval, then re-displays notification. This repeats in a loop, keeping the monitor powered on and active.

EXPECTED RESULT
Both monitors enter power-saving mode and stay in that mode until some given input event.

SOFTWARE/OS VERSIONS
(available in the Info Center app, or by running `kinfo` in a terminal window)
OS: Fedora Linux 40
Linux kernel: 6.11.3-200.fc40.x86_64
KDE Plasma Version: 6.2.1
KDE Frameworks Version: 6.7.0
Qt Version: 6.7.2
Graphics Processor: AMD Radeon RX 6600 XT

ADDITIONAL INFORMATION
Possible duplicate of bug 480026; this was said to be fixed for Wayland.
Primary monitor is LG Electronics LG ULTRAGEAR/101NTVSDW879, using mode 2560x1440@120Hz, adaptive sync ON
Secondary monitor is Acer Technologies Acer H226HQL/LX2AA0024210, using mode 1920x1080@60Hz, adaptive sync N/A