Generic version for csv export (adapted from https://knpuniversity.com/screencast/easyadminbundle/csv-export)

AdminController.php

<?php

namespace App\Controller;

use App\Service\CsvExporter;
use EasyCorp\Bundle\EasyAdminBundle\Controller\AdminController as BaseAdminController;

class AdminController extends BaseAdminController
{
    /**
     * @var CsvExporter
     */
    private $csvExporter;

    public function __construct(CsvExporter $csvExporter)
    {
        $this->csvExporter = $csvExporter;
    }

    public function exportAction()
    {
        $sortDirection = $this->request->query->get('sortDirection');
        if (empty($sortDirection) || !in_array(strtoupper($sortDirection), ['ASC', 'DESC'])) {
            $sortDirection = 'DESC';
        }

        $queryBuilder = $this->createListQueryBuilder(
            $this->entity['class'],
            $sortDirection,
            $this->request->query->get('sortField'),
            $this->entity['list']['dql_filter']
        );
        
        return $this->csvExporter->getResponseFromQueryBuilder(
            $queryBuilder,
            sprintf(
                'export_%s_%s.csv',
                $this->entity['label'],
                date('d-m-Y')
            )
        );
    }
}

CsvExporter.php

<?php

namespace App\Service;

use Doctrine\Common\Collections\ArrayCollection;
use Doctrine\ORM\QueryBuilder;
use Symfony\Component\HttpFoundation\StreamedResponse;
use Symfony\Component\PropertyAccess\PropertyAccess;
use Symfony\Component\Serializer\SerializerInterface;

class CsvExporter
{
    /**
     * @var SerializerInterface
     */
    private $serializer;

    public function __construct(SerializerInterface $serializer)
    {
        $this->serializer = $serializer;
    }

    public function getResponseFromQueryBuilder(QueryBuilder $queryBuilder, $filename)
    {
        $response = new StreamedResponse();
        $entities = new ArrayCollection($queryBuilder->getQuery()->getResult());
        $first = $entities->first();
        $columns = $this->serializer->normalize(
            $first,
            null,
            [
                'groups' => [
                    'export'
                ]
            ]
        );

        if (sizeof($columns) == 0) {
            throw new \LogicException(
                sprintf(
                    'There is no export data available for this entity %s',
                    get_class($first)
                )
            );
        }
        $propertyAccessor = PropertyAccess::createPropertyAccessor();

        $response->setCallback(function () use ($entities, $columns, $propertyAccessor) {
            $handle = fopen('php://output', 'w+');

            // Add header
            fputcsv($handle, array_keys($columns));

            while ($entity = $entities->current()) {
                $values = [];

                foreach ($columns as $key => $column) {
                    $values[] = $propertyAccessor->getValue($entity, $key);
                }

                fputcsv($handle, $values);

                $entities->next();
            }

            fclose($handle);
        });

        $response->headers->set('Content-Type', 'text/csv; charset=utf-8');
        $response->headers->set('Content-Disposition', 'attachment; filename="' . $filename . '"');

        return $response;
    }
}