Provide an EntityReferenceFieldItemNormalizer with options to return content entity labels and config entity IDs.

modules/core/csv/farm_csv.services.yml

@@ -4,3 +4,8 @@ services:
     tags:
       - { name: normalizer, priority: 10 }
     arguments: ['@entity_type.manager', '@entity_type.repository', '@entity_field.manager']
+  farm_csv.normalizer.entity_reference_field_item:
+    class: Drupal\farm_csv\Normalizer\EntityReferenceFieldItemNormalizer
+    tags:
+      - { name: normalizer, priority: 10 }
+    arguments: ['@entity.repository']

modules/core/csv/src/Normalizer/EntityReferenceFieldItemNormalizer.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace Drupal\farm_csv\Normalizer;
+
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\Core\Field\Plugin\Field\FieldType\EntityReferenceItemInterface;
+use Drupal\serialization\Normalizer\EntityReferenceFieldItemNormalizer as CoreEntityReferenceFieldItemNormalizer;
+
+/**
+ * Normalizes entity reference fields for farmOS CSV exports.
+ */
+class EntityReferenceFieldItemNormalizer extends CoreEntityReferenceFieldItemNormalizer {
+
+  /**
+   * The supported format.
+   */
+  const FORMAT = 'csv';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function normalize($field_item, $format = NULL, array $context = []): array|string|int|float|bool|\ArrayObject|NULL {
+
+    // Attempt to load the referenced entity.
+    /** @var \Drupal\Core\Entity\EntityInterface $entity */
+    if ($entity = $field_item->get('entity')->getValue()) {
+
+      // Return content entity labels, if desired.
+      if ($entity instanceof ContentEntityInterface && !empty($context['content_entity_labels'])) {
+        return $entity->label();
+      }
+
+      // Return config entity IDs, if desired.
+      if ($entity instanceof ConfigEntityInterface && !empty($context['config_entity_ids'])) {
+        return $entity->id();
+      }
+    }
+
+    // Otherwise, delegate to the parent method.
+    return parent::normalize($field_item, $format, $context);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function supportsNormalization($data, string $format = NULL, array $context = []): bool {
+    return $data instanceof EntityReferenceItemInterface && $format == static::FORMAT;
+  }
+
+}