Protein powder alone does not increase muscle size. Muscle growth occurs when you engage in strength training exercises and your body responds to the stress by repairing and building muscle tissue. Consuming adequate amounts of protein, including protein powder, can support muscle growth by providing the body with the necessary building blocks (amino acids) to repair and build muscle tissue.
However, simply taking protein powder without engaging in strength training exercises will not increase muscle size. Additionally, consuming excessive amounts of protein powder beyond what your body needs can lead to unwanted weight gain, as any excess protein will be stored as fat.
In conclusion, while protein powder can support muscle growth, it is only one piece of the puzzle. To see an increase in muscle size, you need to engage in strength training exercises and consume adequate amounts of protein as part of a balanced diet and training program.