lo que se indexa son los valores actuales, no todos los valores posibles

app/models/metadata_belongs_to.rb

@@ -77,6 +77,10 @@ class MetadataBelongsTo < MetadataRelatedPosts
     @related_methods ||= %i[belongs_to belonged_to].freeze
   end
 
+  def indexable_values
+    belongs_to&.title&.value
+  end
+
   private
 
   def post_exists?

app/models/metadata_related_posts.rb

@@ -23,7 +23,7 @@ class MetadataRelatedPosts < MetadataArray
   end
 
   def indexable_values
-    values.keys
+    posts.where(uuid: value).map(&:title).map(&:value)
   end
 
   private