Hello.
This solution did not work 100% for my environment. However, it gave me some good tips on how to solve the problem. Let me tell you what I did.
In item 3, I do not have the config.sdf file, but I do have the config.db (in the same directory). I believe that because the CompleteFTP version I am using is 25.0.0, things may have changed a bit.
So I made a backup of the config.db and edited it using DB Browser.
The most valuable tip in your answer was which table I had to edit: NODE.
I realized that the lines in this table that referred to the folders would have to have the content 'c2,0,0' in the Permissions column.
I made the necessary changes to the lines and everything worked out.
Thank you for your support and sorry for my poor English.