well the CCP has effectively incorporated Tiananmen Square into the propaganda. it's become a part of the national narrative - it was "a conflicted time where there were bad decisions made by both sides and they learned from it and are stronger today because of it." - please don't call me a tankie i'm trying to summarize CCP narrative
so it's not really taboo to talk about in China like people assume it is. same thing with the cultural revolution. I read the "three body problem" series by a Chinese author (really good books, if anybody likes sci-fi) and I was amazed at how critical he was of the cultural revolution
and i checked, and he's not an ex-patriate or anything.. he lives in China and released a book that became internationally succesful that was critical of the chinese government during the cultural revolution
it turns out that the CCP actually does allow some level of critique - because they view themselves today as a different party than existed 30 or 50 years ago.
Taiwan, on the other hand, is a current issue. Personally, I feel bad for the taiwanese that don't want to be integrated into China but it does seem like an inevitability at this point.