There's no winning hand when your poker partner is a complete loser, like Russia is. China must be regretting all those warm words ahead of Russian's invasion. Arming Russia wouldn't materially affect the outcome of the war, it's not in a region of Chinese interest, it's a very long supply line, a bunch of Russians losing a war while using the cream of Chinese military tech isn't a great look, and it would piss off all its biggest customers at a time when the Chinese economy is weak.
If the US wanted this thing to end fast, and became less concerned about the risks of escalation because they felt they had to respond to an escalatory threat from China, then they could do that. And that is something China has to think about.
All China can do is try to play the statesman, recoup a bit of prestige where they can, and wait for it to be over - which is pretty much what they are doing. There's no gain for China in this thing continuing for longer than it needs to. And there's no gain in doubling down on being on the losing side.