Gold farming is, at least, based on the premise that there are people who are willing to pay other people money to perform repetitive actions in a video game for them. It's still kind of dumb and it has harmful effects on in-game economies, but at least there's some semblance of money being exchanged for goods and services.
"Play to earn", on the other hand, is based on the premise of cutting out the middleman and having the game developer just straight-up hand players money (or something money-equivalent) for playing their game. How this is even supposed to work from an economic standpoint is a question that I've never seen adequately answered.