China attacking Russia? Seems like a win.
Both China and Russia and Iran and Turkey and Ukraine and all the rest attacking the US would be most logical. This might get the US to stop acting like the Boss of the world and start tending to its own business and stop erring its own borders and attacking its own patriotic citizens.
Being occupied with Ukraine, Russia would almost certainly defend against China with nukes. China has about 500 so say Russia attacked with just 1000, a guess. Both tactical and strategic, to take out Chinese military assets and cities to weaken their ability to continue an aggressive war.
That will be enough to create significant fallout and a moderate nuclear winter. Causing 100s of millions worldwide to die.