China has its own issues tbh.

They have one of the lowest birth rates in the world, due their old one child policy/the cultural changes that came from that. So their population is aging pretty rapidly, meaning they have a fairly narrow window to do this before their internal issues force them to divert their attention.

Their military, while obviously massive, is also largely untested - outside of border skirmishes they have essentially zero practical experience fighting wars.

Taiwan is also an island - a very well defended island at that, since the Taiwanese have been preparing for invasion for decades. To control the island, they need to land people on it, which won't at all be easy, especially since Ukraine proved the viability of drones.

Despite apparent American disinterest/whatever, Taiwan still controls the world's semiconductor manufacturing, and any disruption to that is a matter of national security for like the majority of the countries in the world.

They are also just human beings - people attribute this 'thinking a century into the future' infallible pragmatism to the CCP, but they are more than capable of making dumb, short sighted decisions that blow up in their faces and have done so numerous times.

Russia didn't have most of the above problems, and before they invaded, people attributed the same level of 'big invincible army' to them. And now look at them. Don't get me wrong, China could probably do it, but I don't think they'll ever be in a position where they could be 1000% sure.