Easyadmin csv export using leagueCsv and iterable (inspired from https://symfonycasts.com/screencast/easyadminbundle/global-action)

CsvService.php

<?php
    public function exportAdminData(QueryBuilder $queryBuilder, FieldCollection $fields, string $entityName): StreamedResponse
    {
        $headers = [];
        $properties = array_keys($queryBuilder->getQuery()->setMaxResults(1)->getSingleResult(AbstractQuery::HYDRATE_ARRAY));
        foreach ($properties as $property) {
            $headers[$property] = ucfirst($property);
            foreach ($fields as $field) {
                // Override property name if a custom label was set
                if ($property === $field->getProperty() && $field->getLabel()) {
                    $headers[$property] = $field->getLabel();

                    // And stop iterating
                    break;
                }
            }
        }

        $response = new StreamedResponse(function () use ($queryBuilder, $headers) {
            $csv = Writer::createFromStream(fopen('php://output', 'w'));
            $csv->insertOne(array_values($headers));
            $csv->addFormatter(function (array $data) {
               return $this->serializer->normalize($data);
            });
            $csv->insertAll($queryBuilder->getQuery()->toIterable([], AbstractQuery::HYDRATE_ARRAY));
        });

        $dispositionHeader = $response->headers->makeDisposition(
            HeaderUtils::DISPOSITION_ATTACHMENT,
            sprintf('%s_%s.csv', $entityName, (new \DateTime)->format('Y-m-d_H:i:s'))
        );
        $response->headers->set('Content-Disposition', $dispositionHeader);
        $response->headers->set('Content-Type', 'text/csv; charset=utf-8');

        return $response;
    }

InheritedEasyAdminAbstractController.php

<?php
    public function export(AdminContext $context, FilterFactory $filterFactory, CsvService $csvService): Response
    {
        $fields = FieldCollection::new($this->configureFields(Crud::PAGE_INDEX));
        $filters = $filterFactory->create($context->getCrud()->getFiltersConfig(), $fields, $context->getEntity());
        $queryBuilder = $this->createIndexQueryBuilder($context->getSearch(), $context->getEntity(), $fields, $filters);

        try {
            return $csvService->exportAdminData($queryBuilder, $fields, $context->getEntity()->getName());
        } catch (NoResultException $exception) {
            $this->addFlash('danger', 'Can not export as csv if no line match !');

            return $this->redirect($context->getReferrer());
        }
    }