Cook the elbow macaroni according to package instructions until al dente, about 8–10 minutes. Drain and rinse under cold water.

In a mixing bowl, whisk together mayonnaise, Dijon mustard, and apple cider vinegar until smooth. Season with salt and pepper.

Add the cooled macaroni, diced celery, chopped red onion, pickle relish, and hard-boiled eggs (if using) to the dressing. Stir gently to combine.

Cover and refrigerate for at least 30 minutes before serving to allow flavors to meld.