In a large bowl, add the diced apples, granulated sugar, and lemon juice. Toss gently to coat the apples evenly and prevent browning.
Add the diced celery, halved grapes, and chopped toasted walnuts to the bowl with the apples. Gently mix to combine.
In a medium bowl, use a hand mixer or whisk to whip the heavy whipping cream until stiff peaks form. (Stiff peaks stand straight up and hold their shape when the beaters are lifted.)
Gently fold the mayonnaise into the whipped cream until the mixture is smooth and creamy.
Pour the whipped cream dressing over the apple mixture. Sprinkle with the kosher salt, then gently fold everything together until evenly coated.
Cover and refrigerate for at least 1 hour or overnight to allow the flavors to meld and the salad to chill thoroughly.
Serve cold, as a refreshing side salad or light dessert.