Personally? China. Is it rational, IDK. It's just the largest more capable power at this moment. (particularly their industrial base and ability to out produce weapons / soldiers)

It's not rational. China has even less interest in invading the USA than the USA has in invading China. And I think the USA's interest is effectively zero.

here's more irrational. Because they have >1M single men who will never have a bride. Maybe they want to come and take.

Maybe Xi decides they're mad that we're defending Taiwain.

Maybe the decide to do the inverse vietnam and that the American left deserves to be freed from "Trump" and that communism is freedom and virtuous to give to the American people.

Like I said, probably not rational.

Why would they want to? China’s entire economic model relies on the US remaining a stable, wealthy consumer base for their industrial output. Physically invading your largest customer is a form of economic suicide.

They don't want to govern California; they want to ensure that the global infrastructure, shipping lanes, and institutions run on Chinese technology and standards. From Beijing's perspective, a kinetic war on the US mainland destroys the exact global economy they are trying to lead.

You're assuming economics is the ultimate goal and not just a tool in service of a greater goal.