SUMMARY After the automatic screen lock time, the screen will turn off for a second and then immediately wake back to the desktop session, preventing automatic screen locking. STEPS TO REPRODUCE 1. Set automatic time for screen to dim lock in system settings. (10min to dim and 15min to lock in my case) 2. Wait for the screen to dim and then later to lock automatically. 3. Observe the screen turn off for one second. OBSERVED RESULT Screen wakes again on the open desktop session and does not lock. EXPECTED RESULT Screen should turn off and lock, waking only to the login screen. SOFTWARE/OS VERSIONS Linux/KDE Plasma: 6.19.2-1-default (OpenSuse Tumblweed) KDE Plasma Version: 6.6.0 KDE Frameworks Version: 6.23.0 Qt Version: 6.10.2 ADDITIONAL INFORMATION If the screen is locked manually, the screen will stay on permanently, in the same way described in this bug I had on Vanilla Arch Linux: https://bugs.kde.org/show_bug.cgi?id=506263 This also occurred after the major update to Plasma 6.4 I set this to major severity because it seems to me this is a security issue, as someone would expect their computer to lock when it is unattended after the set time. Apologies however if this classification is misguided.
I'm having the same issue on my machine. Monitor fails to go to sleep and wakes up immediately after a second and repeats the cycle. I've secribed it recently here: https://bugs.kde.org/show_bug.cgi?id=516704 The only way how I managed to resolve this temporarily is to downgrade KWin alone to 6.5.5 and it restored monitor power management properly.
*** This bug has been marked as a duplicate of bug 516704 ***