Not exactly, it actually did work at least once. Protests in HK had been previously successful at stopping a national security law: https://en.wikipedia.org/wiki/National_Security_(Legislative.... The official protest demands were actually pretty modest, and I think even the biggest one (a fully elected government) is actually called for in the Basic Law.
> But as you suggest, the Chinese state is in a position where it doesn't have to care and will happily exterminate the protests.
It's worth noting that one of the protest anthems was "Do You Hear the People Sing?" (https://en.wikipedia.org/wiki/Do_You_Hear_the_People_Sing%3F) from Les Misérables, which is (in part) about a crushed pro-Democracy movement (https://en.wikipedia.org/wiki/Friends_of_the_ABC, https://en.wikipedia.org/wiki/June_Rebellion).
Edit: but that isn't nonviolent protest, it's just leaving your home. It doesn't cause any political change, and it's not at all the logical extreme of nonviolent protest (the logical extreme is stupid, and seems only to have ever been carried out by millenarian cults, but hey ho).
I would love to give those people a home. People seeking freedom are the ones I want in my country, much more than the powerful people trying to seize more power for themselves.
In retrospect, yes, it's fallacious thinking from the protesters if they thought they could successfully press for change just via the protests. But that's in retrospect, previously it might have worked. But as you suggest, the Chinese state is in a position where it doesn't have to care and will happily exterminate the protests. Only answer then is violence, but in this situation the only actors capable of that are other states. In which case, peaceful protest, not fighting back seems the logically correct thing to do -- the protestors require the moral high ground and to focus attention on the issue, which they did very successfully. Whether that has much effect -- probably not, China is ridiculously powerful, but they couldn't do much more (I mean, taken to Gandhian logical extremes, recognition of the failure of the non-violent protest should have been followed mass suicide of all the protesters, which is grotesque but hey, that's Gandhi for you).