pos/pos_meal_voucher/views/view_account_journal.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
Copyright (C) 2020 - Today: GRAP (http://www.grap.coop)
@author: Sylvain LE GAL (https://twitter.com/legalsylvain)
License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).
-->
<odoo>

    <record id="view_account_journal" model="ir.ui.view">
        <field name="model">account.journal</field>
        <field name="inherit_id" ref="point_of_sale.view_account_journal_pos_user_form"/>
        <field name="arch" type="xml">
            <group name="amount_authorized" position="after">
                <group>
                    <field name="meal_voucher_type"/>
                    <field name="meal_voucher_mixed_text"
                        attrs="{'invisible': [('meal_voucher_type', '!=', 'mixed')]}"/>
                </group>
            </group>
        </field>
    </record>

</odoo>