Export file problem in Magento 2.3

If your var/importexportxxx file is blank try;

php bin/magento queue:consumers:start exportProcessor

https://github.com/magento/magento2/issues/23450

You have to run cron by command line as mentioned here: php bin/magento cron:run

https://github.com/magento/magento2/issues/23450#issuecomment-507581035

Then refresh the export page and you should see the file at the bottom.

Replace this below code in app/code/Magento/ImportExport/Controller/Adminhtml/Export/Export.php File

---

This code is working in my application

public function execute()
{
    if ($this->getRequest()->getPost(ExportModel::FILTER_ELEMENT_GROUP)) {
        try {
            $params = $this->getRequest()->getParams();
            $model = $this->_objectManager->create(\Magento\ImportExport\Model\Export::class);
            $model->setData($this->getRequest()->getParams());
            $this->sessionManager->writeClose();

            return $this->fileFactory->create(
                $model->getFileName(),
                $model->export(),
                \Magento\Framework\App\Filesystem\DirectoryList::VAR_DIR,
                $model->getContentType()
            );

            /** @var ExportInfoFactory $dataObject */
            $dataObject = $this->exportInfoFactory->create(
                $params['file_format'],
                $params['entity'],
                $params['export_filter']
            );

            $this->messagePublisher->publish('import_export.export', $dataObject);
            $this->messageManager->addSuccessMessage(
                __('Message is added to queue, wait to get your file soon')
            );
        } catch (\Exception $e) {
            $this->_objectManager->get(\Psr\Log\LoggerInterface::class)->critical($e);
            $this->messageManager->addError(__('Please correct the data sent value.'));
        }
    } else {
        $this->messageManager->addError(__('Please correct the data sent value.'));
    }
    /** @var \Magento\Backend\Model\View\Result\Redirect $resultRedirect */
    $resultRedirect = $this->resultFactory->create(ResultFactory::TYPE_REDIRECT);
    $resultRedirect->setPath('adminhtml/*/index');
    return $resultRedirect;
}