The world we live in now is not one where it’s advantageous to China to be overtly aggressive. We can theorize all day, but looking at Chinese history, they’re just like every other empire in history, and have been quite aggressive in the past. Even the idea of “China” is born out of bloody wars of conquest. I don’t see any reason that they’d be different if given the opportunity.
Materially, they’re xenophobic, like the rest of humanity. Claiming that they’re uniquely not xenophobic is racist in its own way.
They’ve decided before. So has Japan. But you’re missing the point here. It’s not about likelihood of it happening, it’s about what’s possible today vs possible in a changed world.
I’ll try stating it another way. If the US got busy with a civil war for the next few years and I was in a leadership position of say Korea or Japan, I would be pushing for a nuclear program posthaste, because that’s the only real deterrent.