Sorry to be so late coming back but I needed to work on another project and have only just got back. Decided also to reinstall the latest release on a wiped drive (Dell OptiPlex). The result was the same. This is the text from the window that arrives when trying to launch the widget.
file:///home/glyn/.local/share/plasma/plasmoids/org.kde.weatherWidget-2/contents/ui/main.qml:120:5: Type OpenWeatherMap unavailable
file:///home/glyn/.local/share/plasma/plasmoids/org.kde.weatherWidget-2/contents/ui/providers/OpenWeatherMap.qml:18:1: module "QtQuick.XmlListModel" is not installed