If you follow the logic in the post, it is unlikely that there will be a link missing-because Hong Kong is overseas and RMB will not be remitted directly.
Can only be converted into HKD or US dollars to enter Hong Kong for operation.
This is easy to handle. You exchange RMB from 630 yuan into 100 USD according to the official price in Chinese mainland, and then remit it back to Hongkong.
In the account of HK, 100 USD can be converted into 650 RMB according to the exchange rate of RMB in Hong Kong, and RMB will automatically depreciate.
After that, your RMB can only stay in Hong Kong, otherwise there will be a process of "appreciation" when you enter the mainland, and the actual value will be the same. This kind of speculation is not recognized, because everything in Hong Kong denominated in RMB is the mainland market, which directly hedges these spills on the books. Of course, only by issuing RMB settlement stocks and bonds overseas can arbitrage be realized.