According to the logic of degrowth, they should be forced to live in conditions that allow for net zero total emissions of the country they live in. If anything, it should be easier for them because they're a unitary dictatorship, so can degrow by edict. I can't see how not focusing on China in that regard can make sense, they're emitting more currently, they are rapidly increasing their emissions (unlike the US), and they have a great potential to increase it much higher because they have lots more people. Therefore any degrowth strategy should be first and foremost applied to curb their emissions, yet somehow the conversation is always derailed into useless per-capita emissions that do nothing to the planet.
Well first of all, two wouldn't suffice. It's at least three, and I think it might even be four. And with a bunch of mini-Chinas, there'd be more competition for where manufacturing happens, and it could drive emissions down the same way that breaking up a monopoly drives price down.
China's people shouldn't be forced to live in worse conditions because they live in more populous nation. You could split China into two countries with US-level emissions, and we'd be in exactly the same place globally.