China is backing Russia for basically the same reasons Europe is backing Ukraine*: It’s good value for weakening their enemies and getting their allies to owe them. If anything they could afford to do more; aside from sending good vibes their way their relationship with Russia is basically business as usual AFAIK, so they’re actually making money here. Not that I’m defending what they’re doing to be clear, but it makes so much sense geopolitically that it’s hard to imagine them behaving in any other way.

*Europeans might want to back Ukraine for human rights and stuff, but it’s fairly clear that their governments are doing so to keep Russia away.