You make a good point, it isn't only Western nations that buy from Russia, others do as well. Only 10% of U.S. imports came from Russia. But 10% of the total U.S. imports is a huge number of rubles. And C in Russia. But China and a few other nations, to a lesser degree, can buy enough to help fund Putin's military. But you leave out the fact that with exports to Russia banned by the major technology exporting nations, it can't build new weapons or even maintain what it has- which, judging by its performance in Ukraine isn't good -once its supply of parts is exhausted, nor can it develop new weapons technology without certain items banned from export to Russia. China can provide a lot of tech of its own, much of it based on stolen Western technology but it has developed great tech of its own and exceeds the U.S. in some areas.

In short, Putin Russia will maintain a good surplus, on paper, but may not be able to spend it.

As for Biden and China: China refused to say whether it would or wouldn't help Russia resupply its dwindling weapons cache. Why would China give an affirmative yes or no? Because there are two sides at play and Xi knows "secondary" sanctions can be on Chinese citizens' assets, without being the 'shoot yourself in the foot idiocy' the previous guy used- product tariffs that hurt those buying the products far more than it does the seller. But wealthy Chinese insiders have much of their holdings overseas in luxury homes, in factories, in gold bullion; assets that can't be electronically swept away, disappeared, into offshore bank accounts.

China is led by intelligent, world wise men- they know how to keep their cards close to the chest. I think the incredible speed with which Biden grew the coalition of nations cutting off most trade with Russia rattled Xi and made him long for the good old days, when the previous guy was in charge.