I have developed an Forge based application with custom field types. These fields work great in Jira Issues, both in Software and Service Management projects. But when I tried to add these fields to the request form in the customer portal, I ran into two problems.
My fields are always marked as hidden. I made them required to be displayed and tried many other things, but nothing worked.
I found this earlier topic which confirms the behaviour you are experiencing with the Forge custom fields appearing with the Hidden label in Jira Service Management.
That topic also links to the existing feature request to provide the ability to add the fields to the customer request portal. This is where any update in regard to this feature will be provided:
By the way, I think that the arrow in the second screenshot is pointing to a custom field added by another Connect app considering the heroku.app URL is shown.