US can create a new Ukraine in Japan, but the strength difference between Russia and China is too large for it to mean anything.There's no such thing as a war with Japan that lasts a week. Even if you defeat their navy in a week, you'd have to invade or embargo them into a surrender. Perfect opportunity for the US to create a new Ukraine through submarine warfare and getting the Japanese to fight house to house.
Russia struggles with quantity, while China not only has a much larger reserve, they also have a generational quality lead across the board.
With the gdp and production power of 1 Chinese province, even if Russia has a more efficient economy than most EU states, there's simply no way that Russia could realistically approach China in comprehensive national power. If Russia's strength is that they're not deindustrialized, then that strength applies even more for China.
So what puts Russia into a slow attritional war would not necessarily put China in the same situation.
If Japan is the initial aggressor by attacking Taiwan or elsewhere first, no one in the Chinese leadership would have any qualms about leveling major Japanese cities and civilian shelters.