Even with their manufacturing capacity they don't have remotely enough boats to get a nontrivial fraction of those people to the US mainland, and the majority of those people can't swim, so they wouldn't help in taking the US mainland, a requirement to "win" a serious war. Their entire armed forces is also almost completely lacking in combat experience, and in their last skirmish (against some unarmed Indian soldiers in the mountains) 30+ soldiers Chinese tragically drowned, due to the aforementioned lack of swimming ability.
There are some rather bizarre examples such as Gaza attacking Israel, despite getting something like 50% of their electricity and 10% of their fresh water from Israel!
Attacking the supplier of critical civilian and industrial inputs would seem like a mistake nobody in their right mind would make, but... there you go.
I wouldn't be surprised if a future conflict with China over Taiwan would be primarily economic.
They threaten to stop shipping, we threaten to cut off the Internet and their banking, etc...
Similarly, the most knowledgeable experts are predicting that China's strategy with Taiwan will be to simply blockade the island and wait for them to capitulate.
Last but not least, this is also Iran's current strategy. By halting shipping through the Straight of Hormuz, they're waging war on the global economy much more effectively than bombing a few small military air strips in the region.