Can not add field while editing report with sql to generate fields

https://youtu.be/ShtiBBjVmDo this youtube video shows that when trying to add a field in edit mode of a report, there are no fields to choose from. How can I edit a report and add fields when it is based on sql rather than a table or query?
You can download the database here to have a look: Dropbox - LANdpLAN - Simplify your life

Hello,

As stated in another post of yours (Data not showing from field that uses sql on Base report) I have not been able to duplicate. Have no idea where to look in your file and you should post something smaller which shows the problem.