Your questions about SoFi Hong Kong are answered here

When your shares are loaned, SoFi Hong Kong will provide you with the collateral. The collateral will be held in a designated account maintained by a financial institution outside Hong Kong. You will not be able to see the collateral in the app nor withdraw any of the collateral unless there is an occurrence of a default from SoFi Hong Kong. The collateral will be given to you in the form of cash and shall equal at least 100% of the market value of the loaned securities as per the closing price of the day before the last trading day.