I noticed that when you lock the session and leave the system unused, the screen starts turning off after a while, but immediately goes bright again.
Don’t think that I had this kind of issue with Plasma 5.
Edit: Since this is reproducible for me, here are some logs in case they help:
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5277e040] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5277e040] File ended prematurely
13.05.24 21:54 plasmashell kpipewire_logging: PipeWire remote error: -2 unknown resource 5 op:4
13.05.24 21:54 plasmashell kpipewire_logging: PipeWire remote error: -2 unknown resource 5 op:7
13.05.24 21:54 plasmashell kpipewire_logging: PipeWire remote error: -2 unknown resource 6 op:4
13.05.24 21:54 plasmashell kpipewire_logging: PipeWire remote error: -2 unknown resource 6 op:7
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52781d80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52781d80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5282f480] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5282f480] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52781d80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52781d80] File ended prematurely
13.05.24 21:54 systemd Started Systemeinstellungen - Systemeinstellungen.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 ddcutil-service ddcutil-service: Display redetection starting.
13.05.24 21:54 ddcutil-service Display redetection starting.
13.05.24 21:54 ddcutil-service ddcutil-service: Display redetection finished.
13.05.24 21:54 ddcutil-service Display redetection finished.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5282f480] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd5282f480] File ended prematurely
13.05.24 21:54 systemsettings Failed to query platform profile choices "No such object path '/org/kde/Solid/PowerManagement/Actions/PowerProfile'"
13.05.24 21:54 systemd Started dbus-:1.2-org.kde.powerdevil.chargethresholdhelper@4.service.
13.05.24 21:54 systemsettings org.kde.powerdevil.chargethresholdhelper.getthreshold failed: "Charge thresholds are not supported by the kernel for this hardware"
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 systemsettings qrc:/qt/qml/org/kde/systemsettings/CategoryItem.qml:33:13: Unable to assign IconPropertiesGroup_QMLTYPE_82 to IconPropertiesGroup_QMLTYPE_82
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52793f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52793f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 NetworkManager <info> [1715630055.5671] manager: (veth65278ad): new Veth device (/org/freedesktop/NetworkManager/Devices/403)
13.05.24 21:54 NetworkManager <info> [1715630055.5676] manager: (veth51af896): new Veth device (/org/freedesktop/NetworkManager/Devices/404)
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered blocking state
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered disabled state
13.05.24 21:54 kernel veth51af896: entered allmulticast mode
13.05.24 21:54 kernel veth51af896: entered promiscuous mode
13.05.24 21:54 containerd time="2024-05-13T21:54:15.597224423+02:00" level=info msg="loading plugin \"io.containerd.event.v1.publisher\"..." runtime=io.containerd.runc.v2 type=io.containerd.event.v1
13.05.24 21:54 containerd time="2024-05-13T21:54:15.597281650+02:00" level=info msg="loading plugin \"io.containerd.internal.v1.shutdown\"..." runtime=io.containerd.runc.v2 type=io.containerd.internal.v1
13.05.24 21:54 containerd time="2024-05-13T21:54:15.597292741+02:00" level=info msg="loading plugin \"io.containerd.ttrpc.v1.task\"..." runtime=io.containerd.runc.v2 type=io.containerd.ttrpc.v1
13.05.24 21:54 containerd time="2024-05-13T21:54:15.597352215+02:00" level=info msg="loading plugin \"io.containerd.ttrpc.v1.pause\"..." runtime=io.containerd.runc.v2 type=io.containerd.ttrpc.v1
13.05.24 21:54 systemd Started libcontainer container 9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74.
13.05.24 21:54 kernel eth0: renamed from veth65278ad
13.05.24 21:54 NetworkManager <info> [1715630055.7745] device (veth51af896): carrier: link connected
13.05.24 21:54 NetworkManager <info> [1715630055.7746] device (br-015c6a04bc0c): carrier: link connected
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered blocking state
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered forwarding state
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 avahi-daemon Joining mDNS multicast group on interface veth51af896.IPv6 with address fe80::584d:13ff:fe77:a14d.
13.05.24 21:54 avahi-daemon New relevant interface veth51af896.IPv6 for mDNS.
13.05.24 21:54 avahi-daemon Registering new address record for fe80::584d:13ff:fe77:a14d on veth51af896.*.
13.05.24 21:54 org_kde_powerdevil org.kde.powerdevil: org.kde.powerdevil.chargethresholdhelper.getthreshold failed "Charge thresholds are not supported by the kernel for this hardware"
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 systemd docker-9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74.scope: Deactivated successfully.
13.05.24 21:54 systemd docker-9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74.scope: Consumed 10.205s CPU time.
13.05.24 21:54 containerd time="2024-05-13T21:54:23.328861172+02:00" level=info msg="shim disconnected" id=9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74 namespace=moby
13.05.24 21:54 containerd time="2024-05-13T21:54:23.328986725+02:00" level=warning msg="cleaning up after shim disconnected" id=9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74 namespace=moby
13.05.24 21:54 containerd time="2024-05-13T21:54:23.328994572+02:00" level=info msg="cleaning up dead shim" namespace=moby
13.05.24 21:54 dockerd time="2024-05-13T21:54:23.328935181+02:00" level=info msg="ignoring event" container=9c9cc347c9fde0a7ee7ae569ce3be7fb32bb72b546f091d80a1237066f557b74 module=libcontainerd namespace=moby topic=/tasks/delete type="*events.TaskDelete"
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered disabled state
13.05.24 21:54 kernel veth65278ad: renamed from eth0
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 NetworkManager <info> [1715630063.4049] manager: (veth65278ad): new Veth device (/org/freedesktop/NetworkManager/Devices/405)
13.05.24 21:54 avahi-daemon Interface veth51af896.IPv6 no longer relevant for mDNS.
13.05.24 21:54 avahi-daemon Leaving mDNS multicast group on interface veth51af896.IPv6 with address fe80::584d:13ff:fe77:a14d.
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered disabled state
13.05.24 21:54 kernel veth51af896 (unregistering): left allmulticast mode
13.05.24 21:54 kernel veth51af896 (unregistering): left promiscuous mode
13.05.24 21:54 kernel br-015c6a04bc0c: port 1(veth51af896) entered disabled state
13.05.24 21:54 avahi-daemon Withdrawing address record for fe80::584d:13ff:fe77:a14d on veth51af896.
13.05.24 21:54 systemd run-docker-netns-f0c6d5485fa3.mount: Deactivated successfully.
13.05.24 21:54 systemd var-lib-docker-overlay2-9127fb3f4e36e57eff3d8fc815d147acd3c766c125e9ac2896e6aded625df5ad-merged.mount: Deactivated successfully.
13.05.24 21:54 pipewire mod.client-node: 0x555d70e594a0: unknown peer 0x555d70e5a130 fd:45
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52c57f80] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52777100] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52777100] File ended prematurely
13.05.24 21:54 kscreenlocker_greet The cached device pixel ratio value was stale on window expose. Please file a QTBUG which explains how to reproduce.
13.05.24 21:54 kscreenlocker_greet qt.gui.imageio: libpng warning: iCCP: known incorrect sRGB profile
13.05.24 21:54 kscreenlocker_greet qt.gui.imageio: libpng warning: iCCP: known incorrect sRGB profile
13.05.24 21:54 kscreenlocker_greet QMetaObject::invokeMethod: No such method ScreenLocker::AccessDeniedNetworkReply::error(QNetworkReply::NetworkError)
13.05.24 21:54 kscreenlocker_greet QMetaObject::invokeMethod: No such method ScreenLocker::AccessDeniedNetworkReply::error(QNetworkReply::NetworkError)
13.05.24 21:54 kscreenlocker_greet file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/MediaControls.qml:31:13: QML QQuickImage: Blocked request.
13.05.24 21:54 kscreenlocker_greet file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/MediaControls.qml:31:13: QML QQuickImage: Blocked request.
13.05.24 21:54 systemd dbus-:1.2-org.kde.powerdevil.chargethresholdhelper@4.service: Deactivated successfully.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527754c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527754c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd52901580] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 ddcutil-service ddcutil-service: Display redetection starting.
13.05.24 21:54 ddcutil-service Display redetection starting.
13.05.24 21:54 ddcutil-service ddcutil-service: Display redetection finished.
13.05.24 21:54 ddcutil-service Display redetection finished.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 rtkit-daemon Successfully made thread 41996 of process 2627 owned by '1000' RT at priority 5.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 kwin_wayland kwin_core: KWin::LayerShellV1Window doesn't support setting maximized state
13.05.24 21:54 kwin_wayland kwin_core: KWin::LayerShellV1Window doesn't support setting fullscreen state
13.05.24 21:54 plasmashell The cached device pixel ratio value was stale on window expose. Please file a QTBUG which explains how to reproduce.
13.05.24 21:54 kscreenlocker_greet QMetaObject::invokeMethod: No such method ScreenLocker::AccessDeniedNetworkReply::error(QNetworkReply::NetworkError)
13.05.24 21:54 kscreenlocker_greet QMetaObject::invokeMethod: No such method ScreenLocker::AccessDeniedNetworkReply::error(QNetworkReply::NetworkError)
13.05.24 21:54 kscreenlocker_greet QMetaObject::invokeMethod: No such method ScreenLocker::AccessDeniedNetworkReply::error(QNetworkReply::NetworkError)
13.05.24 21:54 kscreenlocker_greet file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/MediaControls.qml:31:13: QML QQuickImage: Blocked request.
13.05.24 21:54 kscreenlocker_greet qt.gui.imageio: libpng warning: iCCP: known incorrect sRGB profile
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 kscreenlocker_greet qt.qpa.wayland: Could not create EGL surface (EGL error 0x3000)
13.05.24 21:54 kscreenlocker_greet qt.qpa.wayland: Could not create EGL surface (EGL error 0x3000)
13.05.24 21:54 kscreenlocker_greet Failed to write to the pipe: Ungültiger Dateideskriptor.
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely
13.05.24 21:54 plasmashell [matroska,webm @ 0x55bd527122c0] File ended prematurely