odoo16/addons/portal/data/mail_templates.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo><data noupdate="1">

    <template id="portal_share_template">
        <div>
            <p>Dear <span t-esc="partner.name"/>,</p>
            <p>You have been invited to access the following document:</p>
            <br/>
            <a t-attf-href="#{share_link}" style="background-color: #875A7B; padding: 10px; text-decoration: none; color: #fff; border-radius: 5px; font-size: 12px;"><strong>Open </strong><strong t-esc="record.display_name"/></a><br/>
            <br/>
            <p t-if="note" style="white-space: pre-wrap;" t-esc="note"/>
        </div>
    </template>

</data></odoo>