You can check the size of files in Plesk File Manager by following these steps:
Open Plesk File Manager and navigate to the desired folder or file.
Select the folder or file for which you want to check the size by checking the checkbox on the left side.
Click the "More" button located above the directory.
After that, the "Calculate Size" button will appear. Click it.
Plesk will calculate the size of the selected folder or file, and the result will be displayed in File Manager. This helps you identify which files are taking up the most disk space on the Plesk server.
