Bring a large pot of salted water to a boil. Add elbow macaroni and cook until al dente, about 8-10 minutes. Drain and cool slightly.

Drizzle apple cider vinegar over warm macaroni, then add grated carrot and onion. Mix gently and let cool for 10-15 minutes.

In a separate bowl, whisk together mayonnaise, milk, and sugar until smooth. Adjust consistency with more milk if necessary.

Pour dressing over cooled macaroni mixture and gently fold to coat. Season with salt and pepper to taste.

Cover and refrigerate for at least 1 hour, preferably overnight to enhance flavors.

Stir before serving. Add milk to thin if needed, and adjust seasoning as necessary.