Cook the Macaroni: Bring a large pot of salted water to a boil. Add elbow macaroni and cook for 10-12 minutes until soft but not falling apart. Drain and rinse with cold water. Refrigerate to cool completely.
Prepare Vegetables: Finely grate carrot and onion using a microplane. Mince celery into tiny pieces.
Make the Dressing: In a large bowl, whisk together 1.5 cups mayonnaise, apple cider vinegar, sugar, salt, pepper, and minced vegetables until smooth.
Combine: Add cooled macaroni to the dressing and toss gently to coat. Add 1/4 to 1/2 cup more mayonnaise if needed for creaminess.
Chill: Cover and refrigerate for at least 1 hour to meld flavors. Stir in extra mayonnaise before serving if dry.
Serve: Serve cold, garnished with grated carrot or chopped scallions if desired.