Whisk softened butter, sweetener, and molasses until smooth.
Mix in pumpkin and vanilla, then add cream of tartar, baking soda, baking powder, salt, and spices. Stir in protein powder and flour. Chill for 30 minutes.
Preheat oven to 350°F (175°C). Mix cinnamon and sweetener for rolling.
Portion dough into 1.5 tbsp balls, coat in cinnamon-sweetener, place on baking sheets, flatten slightly.
Bake for 12-14 minutes until edges are golden. Cool 10 minutes, then transfer to wire rack to cool completely.
Notes
Chilling the dough helps prevent spreading and improves texture.