Bring a large pot of salted water to a boil and cook the macaroni until very tender, slightly past al dente. Drain well.

Transfer the warm macaroni to a large bowl and toss with the apple cider vinegar.

Add the grated carrot and grated yellow onion to the bowl and mix to combine.

In a separate bowl, whisk together the mayo, milk, brown sugar, pepper, and salt until smooth.

Pour the dressing over the macaroni mixture and stir well until everything is evenly coated.

Fold in the chopped green onions.

Cover and refrigerate for at least 1 hour.

Stir before serving and add a splash of milk if needed to loosen the dressing.