I will not say that it is publicly acceptable to discuss Taiwan independence in China, or any other politically controversial matter for that matter. However I also believe that is irrelevant: I think you are overly attributing the forming of opinions to censorship, and not giving enough credit to people's ability to form their own opinions despite censorship.
I don't believe it is irrelevant. You're saying other people are overly attributing opinions to censorship - and you have a Harvard paper (but don't link to it) that may show censorship in China is more based on potential to go viral than on the actual content. How do you think opinions change if ideas can't freely be shared?
And I'm guessing that the definition of censorship in this paper is based on things that are actually removed from the internet, which is not the whole picture. Movies, songs, TV, news, and books all have to be approved by the party before distribution. Education is controlled by the government. There's also the comments that people don't make in the first place because they know it will be censored. That line is always being pushed, and it's purposefully vague. There was a teacher in Sichuan a month or so ago who made a very polite, short comment saying he wondered if the government would consider other strategies on their covid response and he went to jail for 2 weeks!
How do you think people break out of their set opinions? Where did those opinions come from in the first place?
How do opinions change? Through objective reality. Censorship and media control isn't powerful enough. "How Chinese liberals lost the young generation" https://mp.weixin.qq.com/s/erCJHZVLEtnZ4wWbkgij3g
See my other writeup: https://news.ycombinator.com/item?id=28840722