The smartest thing for the US to do about Taiwan is to have TW develop its own nuclear weapons, so that if the PRC invades TW, it becomes an internal Chinese nuclear war where the US is not involved. Chinese annihilating Chinese is not nice, but it's a smart foreign policy move for the US, and it buys the US another 50 years as China rebuilds after its own internal nuclear conflagration with an estimated 200-300M persons killed. That's two generations.

When it came to foreign policy, the British were always good at getting different groups to kill each other. It had to do this because Britain had a small population, and its forces were spread thin. In this kind of situation, it was always best to present Britain as the force keeping the natives from killing each other. Perfect example was the India-Pakistan partition.

The US has to do the same thing because it is not as powerful as it once was. In this kind of situation, the smartest thing to do is to make sure Taiwan has its own nukes because it would remove TW as an obstacle in US-China relations. The US can tell Beijing now that TW has its own nuclear weapons, TW is no longer an obstacle in US-PRC relations.

If Xi is willing to go nuclear in invading TW, then he would reveal himself as a Chinese leader who is willing to use nukes against other Chinese, which would undermine the Party's legitimacy and rule in the PRC. No Chinese leader, not even Xi, would want to have Beijing, Shanghai and Shenzhen wiped out with nuclear weapons in exchange for getting control of Taiwan.