Important: #109493 - Messages in the About module respect their severity 

Description 

Messages added to the "About" backend module through the PSR-14 event \TYPO3\CMS\Backend\Controller\Event\ModifyGenericBackendMessagesEvent were always rendered as an error infobox, no matter which severity the FlashMessage carried. The module now renders each message with its own severity.

Extensions that add messages to that event are affected: The severity of FlashMessage defaults to ContextualFeedbackSeverity::OK , so a message created without an explicit severity - as in the example that came with the event in TYPO3 v12, see Feature: #96899 - New PSR-14 event: ModifyGenericBackendMessagesEvent - is now rendered as a green "OK" infobox instead of a red "error" one.

Event listeners should therefore state the intended severity explicitly:

use TYPO3\CMS\Backend\Controller\Event\ModifyGenericBackendMessagesEvent;
use TYPO3\CMS\Core\Messaging\FlashMessage;
use TYPO3\CMS\Core\Type\ContextualFeedbackSeverity;

final class MyEventListener
{
    public function __invoke(ModifyGenericBackendMessagesEvent $event): void
    {
        $event->addMessage(new FlashMessage(
            'Something needs attention',
            '',
            ContextualFeedbackSeverity::WARNING
        ));
    }
}