That applet (meteo-qt (3.3-1) unstable) was working well until the latest yaru upgrade. (yaru-theme (23.10.0-0ubuntu2) mantic; )
From a terminal i get:
meteo-qt
ERROR: Your openweathermap key has no access to onecall api - 2781: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 2121: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04n doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1800: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04n doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1800: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1544: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1544: meteo_qt
ERROR: Your openweathermap key has no access to onecall api - 2781: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 2121: meteo_qt
INFO: Actual weather status for: Arrondissement de Rennes FR 17.8°
Ressentie 17.9 °C
couvert - 2431: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04n doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1800: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04n doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1800: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1544: meteo_qt
WARNING: The icon weather-many-clouds for the openweathermap icon 04d doesn't exist in the system icons theme 'Yaru-MATE-dark' - 1544: meteo_qt
apport-collect 2039699
Package yaru-theme not installed and no hook available, ignoring
yaru-theme-icon is ignored by launchpad
This is a Mate session on Mantic