In a large mixing bowl, combine the softened cream cheese, powdered keto sweetener, vanilla extract, lemon juice, and a tiny pinch of salt if using. Beat with an electric mixer until completely smooth and creamy. The mixture should look light, glossy, and free from lumps. Properly softened cream cheese is essential here, as cold cream cheese can produce a grainy texture.

In a separate chilled bowl, whip the cold heavy cream using an electric mixer until stiff peaks form. The whipped cream should hold its shape firmly when the beaters are lifted. This step is critical for creating the mousse-like lightness that defines cheesecake fluff. Be careful not to overwhip, as the cream can turn grainy.

Gently fold about half of the whipped cream into the cream cheese mixture using a spatula. Folding rather than mixing preserves the airiness and prevents deflation. Once mostly incorporated, fold in the remaining whipped cream until the texture becomes uniformly smooth, fluffy, and airy.

Carefully fold in the chopped fresh cherries, distributing them evenly without overmixing. Spoon the fluff into serving bowls or dessert glasses and refrigerate for at least 30 minutes. Chilling allows the flavors to meld and slightly firms the texture for a more authentic cheesecake-like consistency.