why can they just sue someone for refusing to buy something
From the article:
As part of the agreements, the Chinese fund granted the remaining minority shareholders an option to require it to purchase their remaining shares for about $9.5 million, now valued at roughly $11 million, by early December 2025.
especially when buying it would be illegal
Legality in country A is completely irrelevant for suing someone in country B.
Also, in many countries having a realistic chance of winning the case is not a prerequisite to suing anyone for anything.


Aufsichtsrat, nicht Vorstand. Und auch nicht zwingend der Ministerpräsident persönlich, wird aber meist so gehandhabt.
https://www.stk.niedersachsen.de/startseite/presseinformationen/ministerprasident-stephan-weil-und-ministerin-julia-willie-hamburg-nehmen-aufsichtsratsmandate-bei-der-volkswagen-ag-wahr-216929.html