Dont know where to put the bug but:

when i configure the timer plasmoid to execute s.t. after the timer finishes, it doesnt happen.

e.g. "/usr/bin/touch /tmp/test"

journalctl contains

    Sep 13 11:34:33 host plasmashell[786]: file:///usr/share/plasma/plasmoids/org.kde.plasma.timer/contents/ui/TimerDigit.qml:43: TypeError: Type error
    Sep 13 11:34:34 host plasmashell[786]: file:///usr/share/plasma/plasmoids/org.kde.plasma.timer/contents/ui/TimerDigit.qml:43: TypeError: Type error
    Sep 13 11:34:35 host plasmashell[786]: qml: is ready to reload - lastReloaded: 1599989218641
    Sep 13 11:34:37 host plasmashell[786]: file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ScrollViewStyle.qml:60:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
    Sep 13 11:34:37 host plasmashell[786]: file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ToolButtonStyle.qml:209:13: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
    Sep 13 11:34:37 host plasmashell[786]: file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ToolButtonStyle.qml:209:13: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
    Sep 13 11:34:37 host plasmashell[786]: file:///usr/lib/qt/qml/QtQuick/Controls/Styles/Plasma/ToolButtonStyle.qml:209:13: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
    Sep 13 11:34:37 host plasmashell[786]: file:///usr/share/plasma/plasmoids/org.kde.plasma.notifications/contents/ui/NotificationHeader.qml:78:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }