Place the cubed potatoes in a large pot and cover with cold water. Bring to a boil over high heat, then reduce to medium-low and simmer for 15–20 minutes, or until tender when pierced with a fork.
Drain the potatoes and transfer them to a large mixing bowl. Allow them to cool slightly while you prepare the other ingredients.
In a small bowl, whisk together the mayonnaise, Dijon mustard, apple cider vinegar, salt, and black pepper until smooth.
Add the chopped hard-boiled eggs, diced celery, and red onion to the warm potatoes. Pour the dressing over the mixture and gently fold everything together until well combined.
Cover the potato salad and refrigerate for at least 1 hour before serving to allow the flavors to meld.
Notes
Serve chilled and enjoy as a side dish at picnics, barbecues, or family gatherings.