Hi,

Inherit receipt screen template for adding button:

<?xml version="1.0" encoding="UTF-8"?>

<templates id="template" xml:space="preserve">

    <t t-name="ReceiptScreen" t-inherit="point_of_sale.ReceiptScreen"

       t-inherit-mode="extension" owl="1">

//Add button

</templates>

/** @odoo-module */

import { ReceiptScreen } from "@point_of_sale/app/screens/receipt_screen/receipt_screen";

import { patch } from "@web/core/utils/patch";

patch(ReceiptScreen.prototype, {

    setup() {

        super.setup(...arguments);

    },

     //code here

});

Hope it helps