Place the diced potatoes in a large pot and cover them with cold water. Bring to a boil over medium-high heat. Once boiling, reduce the heat to medium and cook until the potatoes are tender, about 10-15 minutes. Drain and let cool.

In a large mixing bowl, combine the mayonnaise, Dijon mustard, apple cider vinegar, salt, and black pepper. Mix until smooth.

Once the potatoes have cooled, add them to the bowl with the dressing. Gently fold to coat the potatoes evenly.

Add the chopped celery, red onion, hard-boiled eggs, and sweet pickle relish to the potato mixture. Stir gently until well combined.

If using, fold in the chopped dill for added flavor.

Cover the potato salad and refrigerate for at least 1 hour before serving to allow the flavors to meld.