"Russia cannot support China."
I have no confidence in that claim. During WWII Russia spent tens of millions of lives to defeat Germany. I doubt it has lost 1M so far in this war for it's survival. However, I am confident Trump seeks economic prosperity first, and if he can gain a mutual trade with China - undefiled by illegal infiltration of criminals and fentanyl across the US border - Trump will happily develop an accord with China, with Russia, and even with the EU, if such can be created without military conflict.
Now China wants to dominate Taiwan to dominate the global semiconductor market!
But, Japan intends to compete with China to dominate the global semiconductor market.
So, Japan and China want to dominate Taiwan's semiconductor industry.
Trump seeks a peaceful agreement with China for economic gain, but Japan and China are willing to start a war to seize Taiwan.
Allied together, or each separately to benefit themselves? I do not see any potential today for China and Japan to ally.
Also, the cost to either of taking Taiwan would be far beyond any benefits they might gain, particularly as the chip foundries are mined and will be blown to smithereens if a foreign military gains possession of Taiwan. China has far more economic benefit potential from cooperation with the USA, and so does Japan to continue it, than either has to gain from military hostilities over Taiwan.
Taiwan will never be ruled by the Chinese Communist Party. The Taiwanese would rather be ruled by Japan!