The FileInput component is meant to be used as a part of a form and stores the selected file as a property (column) in the entity (table) which the form is editing. This is the reason it accepts only one file - a table row can have only one value for a column. Downloading the uploaded file isn't something that Radzen provides out of the box. Still I think one can create a custom controller which reads the file from the database and streams it back to the user.
The Upload component on the other hand allows you to select multiple files and store them the way you want - in the file system, in the database etc.
The key here is that FileInput does not replace Upload - it is a way to automatically store files as part of form submission (without requiring custom file storage logic).
Hope this helps!