Facing issue with making DFF on Manage Invoice page as required and fetch the default value fro SAAS

we are not able to make the DFF as a required and non-editable field on Manage Invoice page, also we wanted to fetch the default values based on user login.

When we tried to edit the page (Manage Invoice) using sandbox, then it is not giving option to edit, but on Create Invoice page we can edit

Same DFF we are able to make Required on Create Invoice page but not on Manage Invoice page.

Manage Invoice Page:

Create Invoice Page: