I think it's an interesting point that China bringing the US to account at the UN will show definitively who is on China's side and who is with the anglos. It should make targeted sanctions more effective.
I said it on the Afghanistan thread but I think that China should start supporting at the UN, that the US should pay war reparations on behalf of Afghanistan.
The bridge is already burned and China isnt losing anything if it demands (rightly) that US pays money for the damage it caused to Afghanistan.
Thus China would open another front against US, distracting it from the Indo-Pacific region (win)
Rally support from the Muslim world that it protects their bothers in Afganistan against the imperialism of the US (win)
Massively improve relations between China and Afghan people if they finally see a major power standing with them (win)
Gain important recognition from the small/medium countries that China doesn't support imperialism against weak countries (important win)
Gain the moral high ground, supporting local people and being against occupied forces (win)
Cut a deal with NATO countries so that they wont be dragged on the matter (win for gaining strategic concessions)
Send a shot across the world that from now, the era of unlawful military intervention has ended (big win)
I think we should not read too much into this "
China bringing US to UN court".
The legal case against war crime of US in Afghanistan is an ongoing one. China was and is not the sponsor. What China is doing is merely pushing it forward, but China won't put too much effort on it. So it is more a propaganda act that China may just drop at any moment.
The case is "International Criminal Court investigation in Afghanistan". Here is a UN page about this case in Chinese. You can find it in English.
Afghanistan became a member of ICC since 2003 giving ICC jurisdiction over war crime committed in Afghanistan. US is not a member, but that does not protect Americans in Afghanistan. The case was brought up in 2017 but rejected in 2019 due to the fact that neither Afghanistan government nor US were willing to cooperate. In 2020 US sanctioned the prosecutor of ICC for the case. In 2020 the case was revived after the appeal from the prosecutor. So now there is an active investigation.
This means that China was not part of it. Since China is not a member of ICC, I doubt China would push it too hard. I guess China would beat the drum and blow the whistle but not push it.
Why China voices it today? Because Afghanistan is in Taliban's hand, they will be happy to cooperate with the court against US and former Afghan government. However, the case is against everybody, Taliban would be investigated too if it remains in ICC and allows the proceeding. I don't think Taliban would do that because they are not clean either.
But then why China voices it at all? The answer is "why not" if China don't loose anything either way? Basically China is happy to see the ICC fighting the US and the West. ICC was a creation by the west or countries brainwashed by the west except US. Now it is coming back to haunt the creator. Even if the case fall through it will discredit the western ideology and its creation. It is China calling the west bluff.