China state banks seen selling US dollars to prop up yuan

And another reason is to get rid of a lot of US cash that's being devalued quickly due to inflation.

You'll probably see them stockpiling commodities for the same reason.

If the US can confiscate 300 billion dollars of Russian foreign reserves at the stroke of a pen, all the more reason for China to reduce her own trillion dollars or so of foreign reserves as soon as possible to prevent the same sort of confiscation happening to China. It's called 'hedging'.

They do hold a lot of US debt, and currency. It's very probably win-win.