Canada

I actually don't think China will be a significant benefactor for the US imposed power vacuum. Frankly, their economy is going to shit and they just don't have anything to fill in the bottom that's falling out. Apparently it's starting to look like their population is only a third of what they claimed it to be, and most of their factories are shutting down. Their ghost cities are now not even being completed as everybody's three generations investments are becoming worth less than the dirt it was built on. Even the refugees illegally entering the US through the Mexico boarder last year were majority Chinese.

Russia as well is now a borderline third world country, and the middle east is falling apart with decades of infighting and hate, not to mention that the oil they funded everything with is becoming harder and harder to sell between the green transition and Canada entering their markets as we pull out of the US.

Amazingly, I think that the stagnating EU is going to be the greatest benefactors of this power vacuum, if for no other reason than that nobody else is in a position to take advantage. Maybe Rwanda or another African nation can fill in the gap with how some of them are modernizing at an incredible pace, but considering all the wars they are fighting, not to mention that Rwanda is participating in another genocide right now, I have little expectations there for the next decade or two. South-east Asia and India stands a far better chance of becoming major world powers in that time, but they have their own internal problems to get over before having the power and influence on a world level.

So yea, EU is likely the next world leader and potentially the sole super power as the US crumbles under the weight of a rotting orange.