After reading the English version of the article [0] shared by others in this thread, this look like the adviser has (rightfully or not) panicked and distanced herself from the PhD student (Gerber). The adviser, in her first email, mentions «angry emails from China», but then, when the journalist contacts her, she only refers to a single email from a Chinese doctoral student from Canada.
> The writer [of the email] accuses Gerber of a «racist attack on the Chinese people.» He was referring to a specific tweet: a cartoon that Gerber had posted in response to another user's tweet. It depicted a comic character that had been altered and had stereotyped Chinese features, with yellow skin tone and slit eyes.
> The professor's first email clearly shows that she feared she would no longer be able to obtain a Chinese visa because of Gerber's tweets.
> In the early summer of 2020, Gerber decided to abandon the legal effort. He said he didn't complete the enrollment application because he couldn't find a new adviser: «There was no other professor in the same department with whom I could have finished my work. Changing topics would have meant starting from scratch again after three and a half years. That was out of the question for me.»
The article clearly sides with Gerber on the issue, but I don't think an adviser can be forced to work with a specific PhD candidate. On the other hand, I think this is an important debate:
> [...] Gerber's case demonstrates that China's aggressive foreign policy can in fact influence how academics in Switzerland publicly express themselves, and how they deal with critical comments from their students. It shows that some researchers are willing to restrict their own and others’ activities in order to avoid upsetting China.
[0] https://www.nzz.ch/english/swiss-phd-students-dismissal-spot...