If Russia loses, it may break up into different countries.
China lists all of Manchuria as China- but Russia disputes that.
Manchuria (in red) has extensive oil and gas supplies which would be vital for China which lacks the same type of fossil fuel. People from Manchuria would likely prefer to be part of China than Russia.
If Russia wins, it weakens the Western position. China is also actively working with BRICS to be an alternative to the traditional first-world countries
The longer the war goes on, the more power China ha ve over Russia. If China reduces trade with Russia, the economy of Russia is doomed.