Comrade Xi has learned much over the last five months:
1) In this new technological era Russia’s conventional military, once thought to be a juggernaut, has been unable to successively invade a weaker adjacent country overland. Xi now realizes that his army of combat inexperienced one child soldiers and his locally produced untested ships, planes and equipment just might face a debacle if they try to invade a resisting Taiwan across 90 miles of open ocean. The consequences of failure for Xi, his family and sycophants would be extremely unpleasant.
2) The Chinese now realize that Russia cannot conventionally defend Siberia and its rich underpopulated Far Eastern/Pacific Asian territories. China has always coveted those lands.
Amur River is where the next war will begin, not Taiwan.
Easy pickings, good for bloodying untested troops and new equipment - we’ll see how good the new Chinese MBT T-99A really is:
https://www.youtube.com/watch?v=wy-Lv5N1WYQ
Assuming that Mad Ivan is not going to use nukes to protect those lands.