All of the precursors to make Fentanyl are coming out of China. So while they don't export it directly, they are responsible for it's creation and have refused to work with the WH to crack down on it.
Precursors for fentanyl are common chemicals widely used in pharmaceuticals all over the world. If the issue is exporting country, then simply stop importing the chemicals. US can do this raising tariffs on said precursors
