Wash the potatoes under cold running water and cut them into 1-inch cubes.

Fill a large pot with cold water over the potatoes and add salt. Bring to a boil, then simmer for 15-20 minutes until tender.

In a mixing bowl, combine mayonnaise, Greek yogurt or sour cream, and Dijon mustard. Whisk until smooth, then add chopped dill and parsley.

Add the cooled potatoes and chopped red onion to the dressing. Toss gently to combine.

Season with salt and pepper to taste. Adjust seasoning after chilling, if needed.

Cover the bowl or transfer to an airtight container. Chill for at least 30 minutes before serving.