If it's like Russia, maybe you get paid in bucks but you pretty much must convert them all to RMB immediately. So the bank needs to create all that RMB for all the exporters. Part of it circles back in taxes and stuff. Assuming exporters can't or don't want to spend all that RMB immediately there's now a bunch of RMB in country in some shape or form. A lot probably in banks.
In Russia you have to convert 25-30% of your earnings nominated in foreign currencies (it was 50-80% in 2022, but got relaxed since then) and you do it on a somewhat open market. IIUC in China the requirement is much stricter and the exchange rate is effectively pegged against USD.
Well when back there as a freelancer I know first hand that accepting, legalizing and keeping hard earned foreign dollars was difficult enough that I couldn't justify the effort... and this was even before the war, now that dollars cannot be even bought freely in an open market it's probably worse and more paperwork and roadblocks
