Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the yellow cake mix, eggs, water, vegetable oil, Greek yogurt, 2 teaspoons of cinnamon, and vanilla extract. Using an electric mixer, beat the mixture on medium speed until smooth and well combined, about 2 minutes.
Pour the cake batter into a greased 9x13 inch baking pan. Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Once baked, remove the cake from the oven and allow it to cool in the pan for about 10 minutes.
After the cake has cooled slightly, use a toothpick or skewer to poke holes all over the surface of the cake.
Pour the entire can of sweetened condensed milk over the poked cake, making sure to cover the entire surface.
Cover the cake with plastic wrap and refrigerate for at least 2 hours, or overnight if you have the time.
Once the cake has chilled, remove it from the refrigerator. Spread the thawed whipped topping evenly over the cake.
Slice the cake into squares and serve. Enjoy the delightful flavors of snickerdoodles in every bite!