When you are editing your Custom Form, click on the component and on the right hand side Appearance -> Visibility -> No (Constant).
Of course you can make the visibility dynamic if required. If you have a number of fields that will never be visible it's best to put them all on a new page/tab and hide the entire page/tab so you don't have to set it for every field.
If I do Appearance -> Visibility -> No (Constant). fields won't be visible on the request form. It is not a case.
I want to show them (ex. text fields) on the request form and then hide them on details form on deployments.
Sorry I didn't properly read your question and missed the bit about the Deployment page.
I'll have a play and see if I can figure a way, though given how the product has always handled hidden fields in XaaS I wouldn't hold my breath.