So, es ist erneut passiert, dieses Mal habe ich aber ein Log parat:
Dez 20 14:01:44 ian-zuse-one dbus-daemon[736]: [system] Failed to activate service 'org.bluez': timed out (service_start_timeout=25000ms)
Dez 20 14:01:45 ian-zuse-one xdg-desktop-portal-kde[1317]: xdp-kde-background: GetAppState called: no parameters
Dez 20 14:02:15 ian-zuse-one xdg-desktop-portal-kde[1317]: xdp-kde-background: GetAppState called: no parameters
Dez 20 14:02:47 ian-zuse-one org_kde_powerdevil[1591]: org.kde.powerdevil: Unsatisfied policies, the action has been aborted
Dez 20 14:03:17 ian-zuse-one org_kde_powerdevil[1591]: org.kde.powerdevil: Unsatisfied policies, the action has been aborted
Dez 20 14:03:47 ian-zuse-one org_kde_powerdevil[1591]: org.kde.powerdevil: Unsatisfied policies, the action has been aborted
Dez 20 14:03:56 ian-zuse-one dbus-daemon[736]: [system] Activating service name='org.kde.powerdevil.backlighthelper' requested by ':1.67' (uid=1000 pid=1591 comm="/usr/lib/org_kde_powerdevil " label="unconfined") (using servicehelper)
Dez 20 14:03:56 ian-zuse-one dbus-daemon[736]: [system] Successfully activated service 'org.kde.powerdevil.backlighthelper'
Dez 20 14:04:36 ian-zuse-one kwin_x11[1148]: file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/windowswitcher/WindowSwitcher.qml:62:17: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
Dez 20 14:04:36 ian-zuse-one kwin_x11[1148]: file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ScrollViewStyle.qml:47:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
Dez 20 14:04:36 ian-zuse-one kwin_x11[1148]: file:///usr/lib/qt/qml/org/kde/plasma/components/Highlight.qml:34:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
Dez 20 14:04:37 ian-zuse-one kwin_x11[1148]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 2834, resource id: 14714269, major code: 20 (GetProperty), minor code: 0
Dez 20 14:04:41 ian-zuse-one kwin_x11[1148]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 4084, resource id: 83887955, major code: 18 (ChangeProperty), minor code: 0
Dez 20 14:04:41 ian-zuse-one systemd[1044]: app-libreoffice\x2dwriter-cce04fcb8ca841bab177346b697b1380.scope: Succeeded.
Dez 20 14:04:41 ian-zuse-one kwin_x11[1148]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 4208, resource id: 35651811, major code: 18 (ChangeProperty), minor code: 0
Dez 20 14:04:43 ian-zuse-one kwin_x11[1148]: file:///usr/lib/qt/qml/org/kde/plasma/components/Highlight.qml:34:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
Dez 20 14:04:44 ian-zuse-one kwin_x11[1148]: qt.qpa.xcb: QXcbConnection: XCB error: 3 (BadWindow), sequence: 5855, resource id: 14714536, major code: 20 (GetProperty), minor code: 0
Dez 20 14:05:01 ian-zuse-one dbus-daemon[1066]: [session uid=1000 pid=1066] Activating service name='org.kde.LogoutPrompt' requested by ':1.17' (uid=1000 pid=1179 comm="/usr/bin/ksmserver " label="unconfined")
Dez 20 14:05:01 ian-zuse-one dbus-daemon[1066]: [session uid=1000 pid=1066] Successfully activated service 'org.kde.LogoutPrompt'
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: file:///usr/share/plasma/look-and-feel/org.kde.breath2.desktop/contents/components/UserDelegate.qml:31: ReferenceError: model is not defined
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:406:376: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:407:130: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:408:130: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:408:393: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:409:130: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:410:129: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:411:129: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:412:129: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:413:129: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:413:379: Could not add child element to parent element because the types are incorrect.
Dez 20 14:05:01 ian-zuse-one ksmserver-logout-greeter[5063]: qt.svg: <input>:413:631: Could not add child element to parent element because the types are incorrect.
Sofort nach Auftreten habe ich bei LibreOffice noch gespeichert, danach direkt ALT+STRG+ENTF für den Logout-Dialog. Das waren also die letzten Minuten, bevor der Fehler auftrat.