It's important to note that Stock stepped down because she wanted to. University administrators reportedly supported her as a tenured professor, and did not pressure her to leave.
However, Stock was highly unpopular with students at Sussex. Besides the occasional demonstration against her transphobic ideas (an inconvenience Stock could easily put up with) she had another problem. Students didn't want to take her classes.
I knew a student at Sussex when Stock resigned. They told me most students went out of their way to avoid her, by choosing other classes or maneuvering to take the same class taught by a different lecturer.
This was not because Stock had been silenced, but because of the opposite. Students were well aware of her virulent transphobic ideas and her opposition to the existence of transgender people.
So they chose to study with different professors. Their prerogative. Free speech has consequences.
Nonetheless, the University of Sussex was perfectly willing to allow Stock to continue her work there.
She left because she wanted to. She created a false narrative about being silenced ... all while engaging in quite loud public discourse.