AfterFileStorageTreeItemsPreparedEvent 

Labels 

Tree node labels can be defined to improve accessibility. Each node can have multiple labels, sorted by priority, with the highest priority label taking precedence. All the other labels will be added to the title attribute of the node.

A label can be assigned to a node in user TSconfig using a folder identifier path:

options.folderTree.label.1:/campaigns {
    label = Main Storage
    color = #ff8700
}

Status information 

Status information can be added via the event to provide additional visual cues. Like labels, status information is sorted by priority, and only the highest priority status information is displayed. All status labels are added to the title attribute.

Example 

<?php

declare(strict_types=1);

namespace MyVendor\MyExtension\Backend\EventListener;

use TYPO3\CMS\Backend\Controller\Event\AfterFileStorageTreeItemsPreparedEvent;
use TYPO3\CMS\Backend\Dto\Tree\Label\Label;
use TYPO3\CMS\Core\Attribute\AsEventListener;

#[AsEventListener(
    identifier: 'my-extension/backend/modify-file-storage-tree-items',
)]
final readonly class ModifyFileStorageTreeItems
{
    public function __invoke(AfterFileStorageTreeItemsPreparedEvent $event): void
    {
        $items = $event->getItems();
        foreach ($items as &$item) {
            // Add special label for storage with uid 1
            if ($item['resource']->getCombinedIdentifier() === '1:/campaigns/') {
                $item['labels'][] = new Label(
                    label: 'A label',
                    color: '#abcdef',
                    priority: 10,
                );
                $item['statusInformation'][] = new StatusInformation(
                    label: 'An important information',
                    severity: ContextualFeedbackSeverity::INFO,
                    priority: 10,
                    icon: 'content-info',
                );
            }
        }
        $event->setItems($items);
    }
}

API 

class AfterFileStorageTreeItemsPreparedEvent

Fully qualified name

\TYPO3\CMS\Backend\Controller\Event\AfterFileStorageTreeItemsPreparedEvent

Listeners to this event will be able to modify the prepared file storage tree items for the file / folder tree

getRequest ( )

Returns

\Psr\Http\Message\ServerRequestInterface

getItems ( )

Returns

array

setItems ( array $items)

param $items

the items