The HKIDR allows the Securities and Futures Commission(“SFC”) to identify investors placing orders through intermediaries (e.g. brokers or banks) more effectively and enhance its market surveillance function for better investor protection.
Under the HKIDR, intermediaries must submit their clients ‘identity document information together with the relevant Broker-to-Client Assigned Numbers (“BCAN”) to a secured data repository of the Stock Exchange of Hong Kong (“SEHK”) and the SFC.

You can refer to the following websites:

https://www.ifec.org.hk/web/en/blog/2021/01/investor-identification.page