pos_buttons/static/src/xml/pos_buttons.xml

<?xml version="1.0" encoding="UTF-8"?>
<templates xml:space="preserve">
    <t t-name="pos_buttons.PosButtonsWidget">
        <div class="pos-button">
            <button class="oe_button oe_list_add oe_highlight add-modal" type="button">Crear</button>
        </div>
  </t>
</templates>