Private pages hidden in search but not able to reference in Gravity Forms

Situation:
I have created some ‘private’ Thank You pages which visitors should land on after filling in a Gravity form (on another page).

The problem arises when I try to reference the Thank you page in Gravity forms because it is set to ‘private’. It only lets me select (from a dropdown), pages that are public. There is no facility to type in a url either.

I can’t make the page public because Enfold then shows all the Thank you pages in the search tool (there are 25 in total).

We have to use Gravity forms because they are linked and configured to HubSpot CRM.

The ideal solution is if I can make the pages public and somehow configure the search to eliminate any of my Thank you pages – but how?