social/mail_sendgrid_mass_mailing/views/mass_mailing_view.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <!-- Form view -->
    <record id="view_email_template_sendgrid_form" model="ir.ui.view">
        <field name="name">mass.mailing.sendgrid.form</field>
        <field name="model">mail.mass_mailing</field>
        <field name="inherit_id" ref="mass_mailing.view_mail_mass_mailing_form"/>
        <field name="arch" type="xml">
            <field name="body_html" position="attributes">
                <attribute name="attrs">{'invisible': [('email_template_id', '!=', False)]}</attribute>
            </field>
            <field name="body_html" position="after">
                <field name="html_unframe" widget="html" attrs="{'invisible': [('email_template_id', '=', False)]}"/>
            </field>
            <xpath expr="//field[@name='mailing_model']/.." position="after">
                <field name="email_template_id" domain="[('model', '=', mailing_model), ('sendgrid_template_ids', '!=', False)]"/>
                <field name="lang" attrs="{'invisible': [('email_template_id', '=', False)]}"/>
            </xpath>
            <xpath expr="//notebook/page[1]" position="after">
                <page string="Sendgrid Preview" attrs="{'invisible': [('email_template_id', '=', False)]}">
                    <field name="html_copy" invisible="1"/>
                    <field name="body_sendgrid" widget="html"/>
                </page>
            </xpath>
            <xpath expr="//notebook/page/group[1]">
                <group string="Sendgrid Unsubscribe">
                    <field name="enable_unsubscribe"/>
                    <field name="unsubscribe_text" attrs="{'invisible': [('enable_unsubscribe', '=', False)]}"/>
                    <field name="unsubscribe_tag" attrs="{'invisible': [('enable_unsubscribe', '=', False)]}"/>
                </group>
            </xpath>
        </field>
    </record>
</odoo>