newsupernova/vendor/magento/module-theme/view/frontend/layouts.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
-->
<page_layouts xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/PageLayout/etc/layouts.xsd">
    <layout id="1column">
        <label translate="true">1 column</label>
    </layout>
    <layout id="2columns-left">
        <label translate="true">2 columns with left bar</label>
    </layout>
    <layout id="2columns-right">
        <label translate="true">2 columns with right bar</label>
    </layout>
    <layout id="3columns">
        <label translate="true">3 columns</label>
    </layout>
</page_layouts>