Place potatoes in a large pot and cover with cold, salted water. Bring to a boil and cook until fork-tender, about 20-25 minutes. Drain immediately and let cool slightly.

While potatoes cook, prepare the eggs. Peel the hard-boiled eggs, chop them roughly, and set aside. Prepare all fresh herbs and diced vegetables.

While the potatoes are still warm (not hot), cut them into bite-sized, 1-inch pieces. Place the warm potatoes in a large mixing bowl. Drizzle with apple cider vinegar and toss gently to allow the potatoes to absorb the flavor.

In a separate small bowl, whisk together the mayonnaise, Dijon mustard, sugar (if using), salt, and pepper until smooth. Stir in the chopped parsley, chives, and dill.

Add the chopped eggs, celery, and red onion to the potatoes. Pour the herb dressing over the mixture. Fold gently until everything is evenly coated. Avoid overmixing to keep potato pieces intact.

Taste and adjust seasoning (add more salt, pepper, or a squeeze of lemon juice if needed). Cover the salad and chill in the refrigerator for at least 1 hour before serving to allow the flavors to meld.