Russia can’t afford to finish the invasion of Ukraine, so, how would they be able to join in the fight in another part of rhe world?
And, China and Russia would be risking a much bigger war by going after Taiwan. Do they really want that fight?
The only thing in their favor, is the weakness of the Biden administration, who would likely give them the go-ahead by saying and doing nothing.
So, if China and Russia want to act against Taiwan, they better hurry up, because Trump would have none of it.
That is why they would do. China bailing them out.