I think they probably do a lot of the physical layout, routing, and placement in China, as those are typically labor-intensive activities and China has traditionally been a low-cost market for skilled workers. Over the years, I'm sure engineering salaries there have crept up. Furthermore, much of this work is now becoming increasingly automated.
My sympathies to those employees affected. The economy in China isn't doing very well, lately. Hopefully, they can find jobs quickly. No matter what you think of geopolitics or trade relations between countries, it's still individual people's lives being upturned - that's not a good thing, no matter who or where they are.
Numerous professionals and experts in the GPU industry, nurtured in AMD's ecosystem, have become foundational pillars in China's burgeoning GPU companies. These talents play substantial roles in companies like Bitmain Technologies, TianShu ZhiXin, and more, bringing with them extensive experience and expertise from their tenures at AMD. Meanwhile, the American company is not in the business of nurturing rivals in China, especially if it involves leaking its own IP.
It's not only AMD. Nvidia, Intel, Qualcomm, and others have long had engineering workforces in mainland China. It's traditionally been an easy and inexpensive labor market for tech firms to grow their workforces. They have prioritized that above the long-term strategic threat of training up the competition. Plus, China has long played games around limiting access to their local markets, unless firms established local subsidiaries. Technology-transfer has been an openly-stated goal of such policies.
My own employer had an engineering office in Shanghai, until about 4 years ago. I'm sure the rising trade tensions played into their decision to close that office, but the strength of China's economy also factored into it. They lost their lease on their current office and the new location would've been too far for most existing employees to commute - I guess the real estate market was too hot for them to get anything closer? Meanwhile, our corporate overlords were leaning more in the direction of scaling up operations in India.