You can download files in subfolders from Mass File Download (Record Detail Page Lightning Component) by following these steps:
- Go to the record page where you have added the Mass File Download (Record Detail Page Lightning Component).
- Click on the Settings icon in the right side of the component.
- A settings pop-up window will open.
- Enable the "Download Zip of Files in Subfolders" toggle switch.
- Click on "Done" to save the settings.
With this setting enabled, the files will be downloaded in subfolders within a Zip file.