Provide a ContentEntityNormalizer with an option to explicity include columns.

modules/core/csv/farm_csv.services.yml

@@ -0,0 +1,6 @@
+services:
+  farm_csv.normalizer.content_entity_normalizer:
+    class: Drupal\farm_csv\Normalizer\ContentEntityNormalizer
+    tags:
+      - { name: normalizer, priority: 10 }
+    arguments: ['@entity_type.manager', '@entity_type.repository', '@entity_field.manager']

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

@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\farm_csv\Normalizer;
+
+use Drupal\Core\Entity\ContentEntityInterface;
+use Drupal\serialization\Normalizer\ContentEntityNormalizer as CoreContentEntityNormalizer;
+
+/**
+ * Normalizes farmOS content entities for CSV exports.
+ */
+class ContentEntityNormalizer extends CoreContentEntityNormalizer {
+
+  /**
+   * The supported format.
+   */
+  const FORMAT = 'csv';
+
+  /**
+   * {@inheritdoc}
+   */
+  public function normalize($entity, $format = NULL, array $context = []): array|string|int|float|bool|\ArrayObject|NULL {
+    $data = parent::normalize($entity, $format, $context);
+
+    // If columns were explicitly included, remove others.
+    if (!empty($context['include_columns'])) {
+      foreach (array_keys($data) as $key) {
+        if (!in_array($key, $context['include_columns'])) {
+          unset($data[$key]);
+        }
+      }
+    }
+
+    return $data;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function supportsNormalization($data, string $format = NULL, array $context = []): bool {
+    return $data instanceof ContentEntityInterface && $format == static::FORMAT;
+  }
+
+}