Attacking mainland China seems like a great way to end up in a very bad Nuclear conflict.

China declared decades ago that they follow a No First Use policy in regards to nuclear weapons.

Of course, whether that holds true if boots land on their soil, who knows.

declarations are pointless, but the US is unlikely to put boots on land in china. The last Korean war, the US decided not to do it (invade into chinese territory), and china was much weaker back then.

To take Taiwan China will need air supremacy as well as naval supremacy lack of either one will make it close to impossible. Think about what it took to do d day possible and that was a much shorter crossing and the combined resources of the allies with full air and naval supremacy.