Implement NormalizerInterface::getSupportedTypes().

See https://symfony.com/doc/current/serializer/custom_normalizer.html#improving-performance-of-normalizers-denormalizers

modules/core/geo/src/Normalizer/ContentEntityGeometryNormalizer.php

@@ -128,4 +128,13 @@ class ContentEntityGeometryNormalizer implements NormalizerInterface, Serializer
     return $invalid_count === 0;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getSupportedTypes(?string $format): array {
+    return [
+      GeometryWrapper::class => TRUE,
+    ];
+  }
+
 }

modules/core/kml/src/Normalizer/KmlNormalizer.php

@@ -163,4 +163,13 @@ class KmlNormalizer implements NormalizerInterface, DenormalizerInterface {
     return ['name', 'entity_type', 'bundle', 'internal_id', 'description'];
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function getSupportedTypes(?string $format): array {
+    return [
+      GeometryWrapper::class => TRUE,
+    ];
+  }
+
 }