Merci Nicolas
J'ai activé en mode développement, dans le plugin entre les menus Joomla et le début de la fenêtre du plugin :
eprecated: Joomla\Input\Input implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in /home/lacerealpf/test/libraries/vendor/joomla/input/src/Input.php on line 41
Deprecated: Return type of Joomla\Input\Input::count() should either be compatible with Countable::count(): int, or the #[\ReturnTypeWillChange] attribute should be used to temporarily suppress the notice in /home/lacerealpf/test/libraries/vendor/joomla/input/src/Input.php on line 170
Deprecated: Joomla\CMS\Input\Input implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in /home/lacerealpf/test/libraries/src/Input/Input.php on line 31
Deprecated: Joomla\CMS\Input\Cookie implements the Serializable interface, which is deprecated. Implement __serialize() and __unserialize() instead (or in addition, if support for old PHP versions is necessary) in /home/lacerealpf/test/libraries/src/Input/Cookie.php on line 21
Deprecated: str_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /home/lacerealpf/test/libraries/src/Uri/Uri.php on line 141
Puis dans la fenêtre du plugin lui-même :
Deprecated: strtoupper(): Passing null to parameter #1 ($string) of type string is deprecated in /home/lacerealpf/test/libraries/src/Language/Language.php on line 1172
Mais une fois cliqué sur déclencheur, pas de message hormis le message d'erreur.