China has actually been relatively disinterested investing into Afghanistan [1], even when the US had been footing the security umbrella. Now that any investments might need to also contend with a civil war re-erupting from before the US entered, the numbers to pencil out are even further out of grasp.

Any investment into Afghanistan as a raw materials resource and/or 棲息地, Chinese Lebensraum, would have an ROI of quite a few decades. I don't see why they would economically rationally do that when the Belt and Road Initiative already will net them far more than "just" Afghanistan.

[1] https://asia.nikkei.com/Opinion/The-myth-of-Chinese-investme...