Classes/Controller/FormFlexAjaxControllerV8.php
public function containerAdd(ServerRequestInterface $request, ResponseInterface $response): ResponseInterface
    {
        $GLOBALS['TCA']['tx_imageautoresize'] = include(ExtensionManagementUtility::extPath('image_autoresize') . 'Configuration/TCA/Module/Options.php');
        $GLOBALS['TCA']['tx_imageautoresize']['ajax'] = true;

        // Trick to use a virtual record
        $dataProviders =& $GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['formDataGroup']['tcaDatabaseRecord'];
        $dataProviders[\Causal\ImageAutoresize\Backend\Form\FormDataProvider\VirtualDatabaseEditRow::class] = [
            'before' => [
                \TYPO3\CMS\Backend\Form\FormDataProvider\DatabaseEditRow::class,
            ]
        ];

        $record = [
            'uid' => \Causal\ImageAutoresize\Controller\ConfigurationController::virtualRecordId,
            'pid' => 0,
        ];

        // Initialize record in our virtual provider
        \Causal\ImageAutoresize\Backend\Form\FormDataProvider\VirtualDatabaseEditRow::initialize($record);

        $response = parent::containerAdd($request, $response);
        return $response->withHeader('Content-Type', 'application/json; charset=utf-8');
    }
public function containerAdd(ServerRequestInterface $request, ResponseInterface $response): ResponseInterface
    {
        $GLOBALS['TCA']['tx_imageautoresize'] = include(ExtensionManagementUtility::extPath('image_autoresize') . 'Configuration/TCA/Module/Options.php');
        $GLOBALS['TCA']['tx_imageautoresize']['ajax'] = true;

        // Trick to use a virtual record
        $dataProviders =& $GLOBALS['TYPO3_CONF_VARS']['SYS']['formEngine']['formDataGroup']['tcaDatabaseRecord'];
        $dataProviders[\Causal\ImageAutoresize\Backend\Form\FormDataProvider\VirtualDatabaseEditRow::class] = [
            'before' => [
                \TYPO3\CMS\Backend\Form\FormDataProvider\DatabaseEditRow::class,
            ]
        ];

        $record = [
            'uid' => \Causal\ImageAutoresize\Controller\ConfigurationController::virtualRecordId,
            'pid' => 0,
        ];

        // Initialize record in our virtual provider
        \Causal\ImageAutoresize\Backend\Form\FormDataProvider\VirtualDatabaseEditRow::initialize($record);

        $response = parent::containerAdd($request, $response);
        return $response->withHeader('Content-Type', 'application/json; charset=utf-8');
    }
Render a single flex form section container to add it to the DOM

@param ServerRequestInterface $request
@param ResponseInterface $response
@return ResponseInterface