I agree that we can't provide a definition of "understanding" that would permit automated classification of answers into "shows understanding" and "shows no und

I agree that we can't provide a definition of "understanding" that would permit automated classification of answers into "shows understanding" and "shows no understanding". But the best SE answers actually convey real understanding to the reader; they go beyond the brief provided by the question, and explain a subject with conciseness and lucidity. Nobody could mistake such an answer for ChatGPT output. [I have a suspicion that such really good answers may be mostly several years old; I haven't ever thought to try and quantify that]