whatsapp_web_groups/whatsapp_web_mail/views/mail_template_views.xml

<?xml version="1.0" encoding="UTF-8"?>
<odoo>
    <data>
        <record id="mail_template_view_form_inherit_whatsapp" model="ir.ui.view">
            <field name="name">mail.template.form.whatsapp.web.mail</field>
            <field name="model">mail.template</field>
            <field name="inherit_id" ref="mail.email_template_form"/>
            <field name="arch" type="xml">
                <xpath expr="//page[@name='email_settings']/group[1]" position="inside">
                    <field name="send_whatsapp"/>
                </xpath>
            </field>
        </record>

        <record id="mail_template_view_tree_inherit_whatsapp" model="ir.ui.view">
            <field name="name">mail.template.tree.whatsapp.toggle</field>
            <field name="model">mail.template</field>
            <field name="inherit_id" ref="mail.email_template_tree"/>
            <field name="arch" type="xml">
                <xpath expr="//list" position="inside">
                    <field name="send_whatsapp" optional="show"/>
                </xpath>
            </field>
        </record>

        <record id="mail_template_action_server_activate_whatsapp" model="ir.actions.server">
            <field name="name">Activar WhatsApp</field>
            <field name="model_id" ref="mail.model_mail_template"/>
            <field name="state">code</field>
            <field name="code">
                action = records.write({'send_whatsapp': True})
            </field>
            <field name="binding_model_id" ref="mail.model_mail_template"/>
            <field name="binding_type">action</field>
        </record>
    </data>
</odoo>