Allow different GTM containers per WordPress Multisite subsite

gtm-multisite.php

<?php
/**
 * Plugin Name: Supernova - GTM Multisite
 * Plugin URI: https://www.4property.com/
 * Description: n/a
 * Version: 0.0.1
 * Author: 4Property
 * Author URI: https://www.4property.com/
 * License: GNU General Public License v3 or later
 * License URI: https://www.gnu.org/licenses/gpl-3.0.html
 */

add_action( 'wp_head', 'supernova_pp_google_tag_manager_head' );

function supernova_pp_google_tag_manager_head() {
    $blog_id = intval( get_current_blog_id() );

    $tag_manager = [
        97 => 'GTM-XXXXXX1',
        98 => 'GTM-XXXXXX2',
        99 => 'GTM-XXXXXX3',
    ];
    
    if ( ! isset( $tag_manager[ $blog_id ] ) ) {
        return;
    }

    $gtm_code = "<!-- Google Tag Manager -->
    <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
    new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
    j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
    'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
    })(window,document,'script','dataLayer','" . $tag_manager[ $blog_id ] . "');</script>
    <!-- End Google Tag Manager -->";

    if ( ! is_admin() && $gtm_code ) {
        echo $gtm_code;
    }
}

add_action( 'wp_footer', 'supernova_pp_google_tag_manager_footer' );

function supernova_pp_google_tag_manager_footer() {
    $blog_id = intval( get_current_blog_id() );

    $tag_manager = [
        97 => 'GTM-XXXXXX1',
        98 => 'GTM-XXXXXX2',
        99 => 'GTM-XXXXXX3',
    ];

    if ( ! isset( $tag_manager[ $blog_id ] ) ) {
        return;
    }

    echo '<!-- Google Tag Manager (noscript) -->
    <noscript><iframe src="https://www.googletagmanager.com/ns.html?id=' . $tag_manager[ $blog_id ] . '"
    height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
    <!-- End Google Tag Manager (noscript) -->';
}