OK, maybe I could be the right person to answer this question for you. I am Chinese, and I did my Bachelor's and Master's from Peking University in China, and I got my Ph.D. in the US.
First and foremost, I can surely tell you that right now all Chinese Universities have more strict and rigorous requirements for graduate students (Ph.D. and Master) to get degrees, all because of an actor's plagiarism scandal that happened in 2019 (check Tianlin Zhai plagiarism scandal).
So I assume you plan to go for a Ph.D in China. If you go for a Ph.D. in the top-level universities in China (Project 985 University), or the Chinese Academy of Science, you will have a lot of pressure, same as if you pursue a Ph.D. in the US. You have to publish 3 first-author peer-reviewed manuscripts in SCI-level journals and finish a dissertation written in Chinese.
So back to your question: do you have to follow a 996 schedule? As far as I know, right now many professors wouldn't ask their Ph.D. to do this, however, many Ph.D. worked on weekends voluntarily because they have to make good progress and publish papers. So it really depends on your research progress yourself. I really don't think your professor would force you to follow 996, but if you feel behind or you feel the pressure to graduate, you may force yourself to work on the weekends. When I studied in the US for my Ph.D., my advisor never asked me to follow a 996 schedule, but I worked 6 days a week in order to get more results and publish high-quality papers.
All in all, doing a Ph.D. in top-level universities in China is the same as you pursuing a Ph.D. in the US, Canada, or Europe. You need to take courses, publish papers, pass PhD qualify exam, finish the dissertation, oral defend Ph.D., and eventually and congratulations get your degree.
PS: If you really really plan to purse a graduate school degree in China, try the universities in the 985 Project University List in China. Honestly, I really don't think foreigners would benefit a lot if you enroll in a graduate program that is not on the 985 Project list.