If using rolled oats, pulse them in a food processor until they form a fine flour. Transfer the oat flour to a large mixing bowl.

Add the protein powder and salt (if using) to the oat flour in the bowl. Whisk or stir well with a spoon to combine thoroughly.

Add the almond butter, maple syrup (or honey), and vanilla extract to the dry ingredients in the bowl.

Stir all ingredients together with a sturdy spoon or your hands until a thick, uniform dough forms. The dough should be cohesive and able to hold its shape when pressed. If it's too dry and crumbly, add almond milk 1 teaspoon at a time until the desired consistency is reached. If it's too sticky, add a little more oat flour (1 teaspoon at a time).

Scoop out about 1 tablespoon of dough for each ball. Roll the dough between your palms to form smooth, uniform balls, approximately 1-inch (2.5 cm) in diameter. Repeat with the remaining dough.

Place the rainbow sprinkles in a shallow dish. Roll each protein ball gently in the sprinkles, pressing lightly to ensure they adhere evenly to the entire surface of the ball.

Arrange the finished Birthday Cake Protein Balls on a baking sheet lined with parchment paper. Refrigerate for at least 30 minutes to allow them to firm up. Once chilled, they are ready to serve.