in an earlier sentence, DL used "au passé" when referring to about or of the past, but this sentence did not accept it. What is the difference, if any, between using "du passé" and "au passé" in this context when referring to of or about the past.
Parler du passé - to talk about the past
Parler au passé - to talk using past tense
→ to talk about
→ the past
Mon grand-père n'aime pas parler du (de+le) passé.
→ My grandfather doesn't like to talk about the past.
Parler au passé
→ to talk in/with the past tense ?
Papi doesn’t work for grand father...