Use cases:

• Add custom buttons to existing modules
• Remove or hide buttons based on conditions
• Modify button properties (labels, icons, etc.)
• Reorder buttons

Example event listener:

use TYPO3\CMS\Backend\Template\Components\ModifyButtonBarEvent;
use TYPO3\CMS\Backend\Template\Components\ButtonBar;
use TYPO3\CMS\Backend\Template\Components\ComponentFactory;
use TYPO3\CMS\Core\Attribute\AsEventListener;

final class MyButtonBarListener
{
    public function __construct(
        protected readonly ComponentFactory $componentFactory,
    ) }

    #[AsEventListener]
    public function __invoke(ModifyButtonBarEvent $event): void
    {
        $buttons = $event->getButtons();
        $buttonBar = $event->getButtonBar();

        $myButton = $this->componentFactory->createLinkButton()
            ->setHref('/my-action')
            ->setTitle('My Action')
            ->setIcon($iconFactory->getIcon('actions-heart'));

        $buttons[ButtonBar::BUTTON_POSITION_RIGHT][1][] = clone $myButton;

        $event->setButtons($buttons);
    }
}