We have no idea of knowing, but from what I've heard, they are simply not aware. Almost anything with the phrase "Hong Kong" was censored inside mainland China today.

It's not too hard to find something on Weibo, e.g. this post in support of the police [1] where the highest-upvoted comment at 281 votes condemns the police violence [2].

[1] https://m.weibo.cn/detail/4382509644815287 面对困难，香港警察从不畏惧，坚决捍卫法律尊严！@香港警察

[2] 拿枪射无辜民众及记者，一群警察围殴女孩，拿胡椒喷雾射向老人及外国游客，这样就是维护法治吗

The replies to [2] however, show that nobody believed what she claimed.

Huh? That not everyone agrees doesn't mean nobody believed her. The highest-voted reply complains about censorship. The second-highest talks about the police acting in self-defense. The third-highest fantasizes about shooting ... someone (I initially interpreted it to mean the police, but maybe they actually want to shoot the protesters?)

No, the third one says, if the police really could shoot, why did so many other events [that she mentioned] also happen?

Implying that she lied.

Makes sense, thanks. I still frequently misread Chinese texts that appear completely obvious with hindsight.

Chinese government is paying Chinese people 500 HKD (Hong Kong dollars) to cross the border and counter protest so that they can report there are 800k counter protestors.