It’s a term coined by Cory Doctorow, Sci-Fi writer and ex-EFF, who has been writing about (tech) monopolies, and in particular monopsonies, and how those types of two sided markets originally grow by given users something they need, often for an artificial low price or even free, until they dominate that side of the market, after which they focus mostly on the other side of the market, in this case advertisers, and step by step, slowly disagreeing the reason users originally liked their product… Enshittification.

Doctorow has lots to say, so here’s a link.