Combine warm buttermilk, yeast, and granulated sweetener. Let stand 5 to 8 minutes until foamy. Whisk in egg, melted butter, and salt. Stir in flour gradually to form a soft dough.

Knead on a lightly floured surface for 6 to 7 minutes until smooth and elastic.

Place dough in a greased bowl, cover, and let rise until doubled, about 1 hour. Meanwhile, line a 9×13-inch pan with parchment and combine brown sugar substitute and cinnamon.

Punch dough down and roll into a 16×10-inch rectangle. Spread with the softened butter and sprinkle evenly with the cinnamon mixture.

Roll up tightly from the long edge, pinch seam, and cut into 12 slices. Arrange in pan, cover, and rise until puffed, 35 to 45 minutes.

Preheat oven to 350°F (175°C). Bake 24 to 28 minutes until golden. Cool 10 minutes. Meanwhile, beat cream cheese, butter, powdered sweetener, vanilla, and salt until smooth. Frost rolls while still warm and serve.