For a brief moment thought crossed mind but then when news came out they are considering sending in military to get experience in Ukraine and threatening Taiwan was a reminder that US and China are both enemies.
To your last part, that would likely end hundreds of millions if not billions of lives. The world population is several times larger than it was during the second world war. A conflict at scale between the United States and China would absolutely be a global conflict.
For no reason other than to illustrate how many lives another world war would take, World War 2 resulted in the loss of life of at least 3% of the world population. That figure in 1946 was somewhere in the range of 70 to 80 million. 3% of the global population today would be 246 million people.
I don't point this out to be snide, just to say that it is absolutely a worst possible case scenario if the United States and China go to war against each other. It would affect the lives of every human being on earth. Those nations do not share land borders. It would mean widespread invasion and destruction of other nations in both hemispheres.