Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line it with parchment paper for easy removal later.

In a mixing bowl, whisk together the flour, sugar, baking powder, salt, and cinnamon (if using) until well combined.

In another bowl, beat the softened butter until creamy. Add eggs one at a time, mixing well after each addition. Stir in the vanilla extract and milk until combined.

Gradually combine the wet and dry mixtures, stirring until just incorporated. Be careful not to overmix; a few lumps are perfectly fine.

Gently fold in the blueberries until evenly distributed throughout the batter. The batter will be thick and lumpy, which is a good sign!

In a small bowl, combine the softened cream cheese, powdered sugar, and vanilla extract. Mix until smooth and creamy.

Pour half of the batter into the prepared pan. Dot it with half of the cream cheese mixture, using a butter knife to create swirls. Repeat with the remaining batter and cream cheese mixture on top.

Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean.

Allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.