Edit the form defaults?

It is mentioned that the forms can be edited. But from what I can tell, it’s only a few things you can edit, like have the same bank account in the payment form show up all the time when you want to put in a new payment.
I had hoped you could add new dropdown list in that page for instance. Yes, I know, you can have custom fields, but they always appear at the bottom of that page, you can not really “edit” the page layout.
But when I go to the Northwind payment page, where payments have been added, I can see that there are a dropdown list added in the page between account and description.

Something like that is what I’m after.
I’ve looked the explanation page (of the guide for editing form defaults) up and down but can not see any way to do this.
Does that only work in the cloud edition or am I missing something here?

You cannot edit fields present, only content of fields already defined for the form. And not the layout of the entry screen.

The field on the form you show is the Payee field and is on all Receipt & Payment forms.
There is no drop-down list.
As you enter data, it has a suggested entry from the list of previous Payees entered

0000000 Bug 2a

That is because the Account mentioned is a Control Account and has associated sub fields

The Receipt and Payment form only has the ability to add “custom fields” which you have noted only appear at the bottom, it does NOT have ability to add “line custom fields” - that is fields within the item / account / description line.

Unlike the Purchase or Sales Invoices form which does have the ability to add “line custom fields”.