So do you want the KNIME WebPortal to list automatically n download buttons where n is the number of files that are found on S3 on workflow execution?
If that is the case you could make a network of empty table switches:
only the right amount of widgets is activated depending on how many urls are listed in the input table.
That is tedious to build and you could always have the case where you have way more download buttons than widget/quickform nodes in the workflow.
You could use a network of empty table switches of 5 widget/quickform file download node, then loop it with a recursive loop node (example here of recursive view : https://kni.me/w/20LQKtn68R7_89fH) so you hit “next” on the KNIME WebPortal and you sort of scroll through the downloads.
If you want a single button that downloads multiple files via a browser, well i am not even sure if that is possible with any tool as web browser might have a protection for such a button that spams downloads and fills your folder…
Did I get your question correctly?
Let me know