As you mention your report inherits from the standard invoice report, I assume you already know that the standard invoice layout is a Qweb view named report_invoice_document
and you have already defined a template like
<template id="your_module.report_invoice_document" priority="50" t-name="Your Module - Modifications to the Standard Invoice Layout" inherit_id="account.report_invoice_document">
<xpath expr="//div[hasclass('page')]" position="inside">
<div>Your content</div>
</xpath>
</template>
So the only issue is to fine tune both the XPath expression and the position. The whole report is inside a <div class="page">
tag, so using the above xpath
tag will put your content just before the report's end.
report_qweb_element_page_visibility
module in Odoo apps. – KbiR