Never forget that one thing driving China’s motives is their fascination with what they call the century of humiliation. Their leaders will do just about anything to get back land they lost during that century (as well as other things, like get even with the west for the 1st and 2nd Opium Wars).
This maybe too simple of an concept, but China is like a narcotic to Russia, Russia needs the industrial power of China to keep the weapons flowing in order to sustain itself in the war with Ukraine.
So long as China is solidly behind Russia, Russia will never run out of weapons, combined with their own industrial output, Russia has all they need to keep fighting indefinitely.
China is also like a loan shark, they keep aiding Russia in this war but at some point, in the future, all that aid will get called in and that means China will start making demands of Russia for return of land from generations ago.