More specifically, what is the oldest evidence of human awareness of what we now call the Pythagorean Theorem?
The phrase, "evidence of human awareness" was used to exclude a different question of when was the first proof made. It also constrains answers to those based on artifacts. (Artifacts form the basis of our knowledge of ancient history.) Each artifact can have different interpretations. The dates of the artifacts have errors/uncertainties. So, the question boils down to, of all the artifacts ever in existence, which probably has the earliest date that also is good evidence of a human being aware of the Pythagorean Theorem?