They don’t need to do a D-Day type of invasion. they just need to impose a blockade like the Houthis have done with the Suez Canal.
The US Navy can’t do anything to stop the Houthis after 6 months. How do you think they will do against a PRC blockade ?
In response to the declaration of a Chinese blockade of Taiwan, the US could announce a counter-blockade of China and quickly sever her trade ties and seize her overseas assets.
If necessary, after several months of preparation, the US could then break the blockade and send a naval relief force to Taiwan's aid. My surmise is that China would back down rather than risk a naval engagement.