Preheat the oven to 400 degrees F (200 degrees C). Coat a 10x15-inch baking sheet with cooking spray.

Bring a large pot of lightly salted water to a boil. Cook elbow macaroni in the boiling water, stirring occasionally until cooked through but firm to the bite, 8 minutes. Drain.

Melt butter in a large saucepan over medium heat. Add flour; cook and stir until slightly toasted and fragrant, about 2 minutes. Whisk in enough milk to reach desired consistency; simmer until thickened, whisking constantly, 2 minutes. Stir in processed cheese cubes until melted and smooth, stirring often.

Unroll pizza crust; place on the prepared baking sheet. Spread about 3/4 cup cheese sauce on crust. Stir cooked macaroni into remaining cheese sauce; spoon onto crust in an even layer. Sprinkle pizza with mozzarella cheese.

Bake in the preheated oven until crust is lightly browned and mozzarella is golden brown, about 15 minutes.