Theoretically, soy milk should be a mixture of soy milk and milk

The soy milk powder in supermarkets should be milk powder plus some bean extracts and then add sugar or something. It is definitely nutritious, but the protein content may not be as high as real soy milk.

In addition, the protein in soy milk is better absorbed than that in beans. It is still recommended that you eat processed soy products! Tofu, yuba, etc. are also available!