Enofirm-Temp/extra-addons/NextZen/nextzen_approval_configuration/views/approval_request_views.xml

<?xml version="1.0" encoding="utf-8" ?>
<odoo>
    <record id="nxz_approval_request_view_form_config" model="ir.ui.view">
        <field name="name">nxz.approval.request.form.config</field>
        <field name="model">nxz.approval.request</field>
        <field name="inherit_id" ref="nextzen_approval.nxz_approval_request_view_form" />
        <field name="arch" type="xml">
            <xpath expr="//field[@name='definition_id']" position="after">
                <field name="source_document" readonly="1" />
            </xpath>
        </field>
    </record>
</odoo>