Documents show have 4GB but there is no file in it
The amount of data being shown is the total amount of storage the documents take up on your local disk. You are not seeing any files since it is only displaying large files, as seen by the tab bar below the "Documents" header where "Large Files" is selected. This means there are no large documents on your Mac, but there may be many small files that are taking up the 4.11 GB.

To see all the files that may be taking up storage on your Mac, click "File Browser" in the tab bar under the "Documents" header. This will show all the files in the root directory of your Mac, so you can clear them out. However, I would not recommend removing files from the "Library" folder unless you know what you are doing. This folder can contain system files that are essential to running certain apps.