Will applications such as Power BI, Crystal Report, MS Access, and Excel or my custom application connected to QODBC store my QuickBooks Data? Can anyone read that data?

QODBC will provide the requested data to the calling application.

It then depends on the application and you to protect your data.

After providing the data to the calling application, QODBC has no control over the calling application and cannot enforce encryption.

Example. You have extracted Invoice data from QuickBooks using QODBC in an Excel file. Now, it is your responsibility to protect the Excel file.