Although @stefan1959 has answered the question, I’ll elaborate:
It is a FILE manager, not a DIRECTORIES manager. When you’re using file manager it assumes you’re going to select one or more files, not a directory architecture.
So when you click on a folder, it’s going to open that folder thinking that you’re looking for THE file or files you want to upload.
That’s why the thing to do is zip the folder you want to move. Then go to where you want that folder to be on your server. Upload that zip file to that location. Then you can select that zip file, unzip it and there it is.