China has easy access to Russia, but it was also a major buyer of Iranian and Venezuelan oil. Can the Russian pipelines scale up to cover that at short notice?

Estimates for China’s strategic reserve seem to be 1.3 billion barrels, which is about three or four months of imports. That’s not very different to the EU requiring members to have 90 days in reserve

To be clear, I do not think that China is about to collapse over this or anything like that. It’s a functioning country with a generally competent government. I just think that the (implied) assessment of China being functionally isolated from the pressures you describe Japan and the EU facing is wrong

because they are massive net importers of petroleum

So is China, it imports more oil than any other country by a fair margin and as far as I can tell a bit more than the EU27 collectively do as well