Users with no roles are not allowed to see the attachment icon and are unable to attach a file on a task record in the widget form.
Steps to Reproduce
This problem has been fixed in Kingston, where the relevant service portal widget has been replaced.
As a workaround on previous releases, attach the required files from the standard native UI. Also, users with Admin or ITIL roles are able to access and use the attachment icon on the service portal.
Related Problem: PRB1083808