Make the dressing: In a small bowl, combine sour cream, mayonnaise, olive oil, lemon juice, and salt and pepper. Mix well until smooth and evenly combined. Set aside.
Cook the carrots and potatoes: Peel and cut carrots and potatoes into ½-inch cubes. Place them in a pot of cold water and bring to a boil. Cook for about 10–12 minutes, or until soft enough to pierce easily with a fork. Drain, let cool completely, and set aside.
Prepare the other vegetables: While the carrots and potatoes are cooking, cut onion, celery, and apple into ½-inch cubes. Soak them in water for about 5 minutes to remove the sharp bite, then drain well using a colander.
Cut the beets.Cut the vinegar beets into ½-inch cubes and set aside.
Combine everything.In a large bowl, add all the diced vegetables (carrots, potatoes, onion, celery, apple, and beets). Pour in the prepared dressing and toss gently until everything is evenly coated.
Cover and refrigerate for at least 2 hours (or overnight) to let the flavors blend. Give it a quick mix before serving.