Democracy isn't when you have multiple parties. It's when you elect people to govern. Many americans think that America has a uniparty, despite all appearances.
I feel like you have it the wrong way around. There are a lot of political setups where you "elect someone" that are absolutely not democracies. I can be an authoritarian supreme leader who allows citizens to elect who will run their province (from my choice of candidates of course!) and I really don't think it's reasonable to claim that this situation is a "democracy".
It's autocracy with democratic characteristics.
I agree your criticisms of democracy in the US and Taiwan have some validity but in terms of deciding whether China might be a democracy or not they seem like whataboutism.
You get to vote sometimes but there's only one party...