China is probably not yet ready to mount a complex air-sea invasion of Taiwan, with the mighty USA at its back. But it would have no real difficulties making land invasion into Russia.
Taiwan.. not yet, too hard, but Russia is officially a GO opines our dunk tank subject, further free military advice for China can be found in the article
Ukraine's not even a supply center; Russia needs to take Budapest by the end of autumn if they want to build this year.