Hello,

This will hide the  "Add a line" in transfers when the status is done/cancelled.

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="view_picking_form_inherit_restrict_new" model="ir.ui.view">
        <field name="name">stock.picking.restrict.new</field>
        <field name="model">stock.picking</field>
        <field name="inherit_id" ref="stock.view_picking_form"/>
        <field name="arch" type="xml">
            <xpath expr="//field[@name='move_ids_without_package']" position="attributes">
                <attribute name="options">{'create':[('state','not in',['done','cancel'])]}</attribute>
            </xpath>
        </field>
    </record>
</odoo>