What's an example of a specific change you're trying to make which you aren't able to figure out how to make?

I am not able to edit the form such that users belonging to a certain group are not able to change the state ie: "close" a task.
Having read into other similar situations ( T11207 ) and reading that your solution is to use custom forms I began investigating custom forms.

Have you tried using Lock/Hide Fields to hide the "Status" field?

From what I understood, if I edit the built-in form, It would apply globally, so I only wanted that field hidden, if it was a new form. which is what I was trying to create.

I cannot edit the form to have hidden fields for some, but not others.. surely?

In T12321#213543, @epriestley wrote:

This does not describe a bug in Phabricator. I've reviewed the documentation and believe it is already sufficiently clear in describing how to accomplish what you're trying to accomplish. Particularly, I don't see anything in the documentation which is misleading, or suggests that the workflow you're using is the correct way to accomplish your goal -- it isn't, and the documentation describes the correct workflow. See Support Resources for other support resources.

Sorry for adding you as a subscriber.

But what is described in the documentation is not what is happening, I spent hours trying to do this.
It certainly seems like a bug as I cannot create a new "create task" form, like you have in your phabricator installation here.
I have followed documentation step by step on a new Phabricator build in Phacility.
I am only presented with this form to edit: Name, Preamble, Visible to.

I'm sorry to persist, but how is this correct?
According to documentation I should be able to create new forms.
What use is a form with three fields that doesn't even nearly represent the new form I need to create.

Maniphest -> Create Task -> Configure Form -> View Form Configurations -> Create Form.

I am expecting a Similar form to "Create Task" to appear, but be editable.

IF: a form displaying name, preamble, visible to, is all that is meant to appear.
And saving this form, or editing it results in a form that displays these fields.
then indeed that is correct functionality, as that is what happens.

Like wise if I click on "View form configurations, and change path to
Transactions -> Edit Engines -> Configurations -> Forms

Once I press edit form configuration I am still only presented with those three fields.

There is no way to press "Edit form configuration" and not be presented with those three fields.

There is no way to create a new form using anything but a "three field form" Name, preamble, "visible to" as the base.

I have tried every combination I can think of, I am always led back to the same form with only three fields.

This is all I am able to create:

Here's what I just did on a new Phacility instance:

Maniphest → Create Task → Configure Form → View Form Configurations → Create Form

Create New Form (Button)

All the fields are there.