Russia winning slowly or quickly is in both China's interests but Russia losing isn't. Russia being defeated leads to NATO turning their entire attention to the Pacific or a regime change into a puppet that opens their airspace to NATO overflight.
The best case scenario for China is Russia becomes something like a nuclear armed and more independent Canada, but with aligned economic and foreign policies with China. Most of all, Russia guaranteeing that their airspace will be closed to foreign incursion, and that their markets remain open from political interference, is important. Russia winning in Ukraine slowly or quickly doesn't matter for that, only losing does.
Russia is a major nuclear power, arguably with even more openly declared nukes than even China. That means they have hostage taking power over the world or at least the whole west.
Yes, Russia will lose heavily in reputation, but they will not be couped or lose any core territory. Anymore than US was couped after Korea or Vietnam.
If Russia is defeated, they will go back to Feb 24 borders, declare that Ukraine has already been "de nazified" and threaten to attack with the full Russian army + tactical nukes if Ukraine dares to cross the Feb 24 borders.
Perhaps given how badly the Putin/Yeltsin successor government has handled the question of modernization in the Russian economy, a shake up against United Russia is in Chinese interests. China needs strong allies, not stagnating countries with Western levels of corruption and horrible procurement issues.
Maybe an Ukraine leaning ceasefire can bring about the pressure needed to revive the communists. In order to kickstart the exporting of social revolution again, a retreat to Feb 24 for Russia is a small price to pay. The question is, is the CPC ready to take on an international organizational role?