odoo16/addons/mail/wizard/mail_template_preview_views.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <data>
        <record id="mail_template_preview_view_form" model="ir.ui.view">
            <field name="name">mail.template.preview.view.form</field>
            <field name="model">mail.template.preview</field>
            <field name="arch" type="xml">
                <form string="Email Preview">
                    <h3>Preview of <field name="mail_template_id" readonly="1" nolabel="1" options="{'no_open' : True}"/></h3>
                    <div class="alert alert-danger" role="alert" attrs="{'invisible' : [('error_msg', '=', False)]}">
                        <field name="error_msg" widget="text"/>
                    </div>
                    <field name="no_record" invisible="1"/>
                    <div class="container">
                        <div class="row">
                            <span class="col-md-5 col-lg-4 col-sm-12 ps-0">Choose an example <field name="model_id" readonly="1"/> record:</span>
                            <div class="col-md-7 col-lg-6 col-sm-12 ps-0">
                                <field name="resource_ref" readonly="False" class="w-100"
                                    options="{'hide_model': True, 'no_create': True, 'no_open': True}"
                                    attrs="{'invisible': [('no_record', '=', True)]}"/>
                                <b attrs="{'invisible': [('no_record', '=', False)]}" class="text-warning">No record for this model</b>
                            </div>
                        </div>
                        <div class="row">
                            <span class="col-md-5 col-lg-4 col-sm-12 ps-0">Force a language: </span>
                            <div class="col-md-7 col-lg-6 col-sm-12 ps-0">
                                <field name="lang" placeholder="Select a language" class="w-100"/>
                            </div>
                        </div>
                    </div>
                    <group>
                        <field name="subject"/>
                        <field name="email_from" attrs="{'invisible':[('email_from','=', False)]}"/>
                        <field name="partner_ids" widget="many2many_tags" attrs="{'invisible':[('partner_ids', '=', [])]}"/>
                        <field name="email_to" attrs="{'invisible':[('email_to','=', False)]}"/>
                        <field name="email_cc" attrs="{'invisible':[('email_cc','=', False)]}"/>
                        <field name="reply_to" attrs="{'invisible':[('reply_to','=', False)]}"/>
                        <field name="scheduled_date" attrs="{'invisible':[('scheduled_date','=', False)]}"/>
                    </group>
                    <field name="body_html" widget="html" nolabel="1" options='{"safe": True}'/>
                    <field name="attachment_ids" widget="many2many_binary"/>
                    <footer>
                        <button string="Close" class="btn-secondary" special="cancel" data-hotkey="z"/>
                    </footer>
                </form>
            </field>
        </record>

        <record id="mail_template_preview_action" model="ir.actions.act_window">
            <field name="name">Template Preview</field>
            <field name="res_model">mail.template.preview</field>
            <field name="binding_model_id" eval="False"/>
            <field name="type">ir.actions.act_window</field>
            <field name="view_mode">form</field>
            <field name="view_id" ref="mail_template_preview_view_form"/>
            <field name="target">new</field>
            <field name="context">{'default_mail_template_id':active_id}</field>
        </record>

    </data>
</odoo>