1. Fentanyl has legitimate pharmaceutical uses.
2. There are many, many, many legal manufacturers of Fentanyl, across the world, including Bayer, Johnson&Johnson, Meiji Seika Pharma (Japan), and yes, Chinese manufacturers. Some legal fentanyl ends up getting diverted into illegal channels.
3. There are also many, many, many illegal manufacturers of Fentanyl, again, across the world.
4. The reason for why China has had an outsized share of illegal fentanyl production is that for many years, it (and its derivatives and precursors) has not been a controlled substance.
5. Fentanyl is now a controlled substance in China, and it, its precursors, and its derivatives have been controlled substances since May 2019.
https://www.foxnews.com/media/opioid-crisis-fentanyl-china-m...
If you want to stop fentanyl, the best thing to do is to figure out what chemicals are used exclusively in fentayl production and build an international coalition to ban those. Unfortunately many people just don't appreciate this kind of sophistication and prefer an easier blame game.