Start by placing whole red potatoes in a large pot filled with salted cold water. Bring to a boil over high heat, then reduce to medium and cook until fork-tender, about 15-20 minutes. Drain and let cool before chopping into bite-sized pieces.

In a large mixing bowl, combine mayonnaise, sour cream, apple cider vinegar, lemon juice, Dijon mustard, kosher salt, and black pepper. Whisk until smooth and well blended.

Add the chopped potatoes, diced celery, finely chopped red onion, and fresh dill to the dressing. Gently mix using a spatula, ensuring potatoes are coated without mashing.

Cover with plastic wrap or transfer to an airtight container and refrigerate for at least 30 minutes before serving.