Place the diced potatoes in a large pot and cover with water. Bring to a boil and cook until tender, about 15-20 minutes. Drain and let cool.

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

In a large bowl, combine the cooled potatoes, celery, red onion, pickle relish, and chopped hard-boiled eggs. Pour the dressing over the mixture and gently fold to combine.

Cover the potato salad and refrigerate for at least 1 hour before serving. Garnish with fresh parsley before serving.