If you watch this video you will see that it is not intuitive to adding multiple files in HubSpot forms associated with the customer portal.
This video outlines the issue: Screen Capture on 2022-09-01 at 14-03-12.mp4 - Droplr
If it worked the way the file attachment worked for this post it would be great. Screenshot on 2022-09-02 at 10-49-21.png - Droplr