Inspect wp-admin/network.php and wp-admin/includes/schema.php files. You can create a condition based on WP_INSTALLING_NETWORK

Inspect wp-admin/network.php and wp-admin/includes/schema.php files. You can create a condition based on WP_INSTALLING_NETWORK

Update:

if (is_admin()){
    /* First Step */
    if (!defined( 'WP_ALLOW_MULTISITE')){
            $current_wp_config = file_get_contents(ABSPATH . 'wp-config.php');
            
            $my_defines = "/* First we put WP_ALLOW_MULTISITE  */\r\n" .
                    "define('WP_ALLOW_MULTISITE', true); \r\n";
                    
            $current_wp_config = str_replace("/* That's all, stop editing", $my_defines . "/* That's all, stop editing", $current_wp_config);       
            file_put_contents(ABSPATH . 'wp-config.php', $current_wp_config);   
    }   
    /* Second Step */
    if (!defined("WP_DEFINES_IMPORTED") && defined("WP_INSTALLING_NETWORK") && $_POST){
        $current_wp_config = file_get_contents(ABSPATH . 'wp-config.php');
        
        $my_defines = "/* Now we define */\r\n" .
            "define('WP_DEFINES_IMPORTED', true); \r\n" .
            "define('MULTISITE', true); \r\n".
            "define('SUBDOMAIN_INSTALL', true); \r\n".
            "define('DOMAIN_CURRENT_SITE', '". get_clean_basedomain() . "'); \r\n".
            "define('PATH_CURRENT_SITE', '". parse_url(  trailingslashit( get_option( 'home' ) ), PHP_URL_PATH ) . "'); \r\n".
            "define('SITE_ID_CURRENT_SITE', 1); \r\n".
            "define('BLOG_ID_CURRENT_SITE', 1); \r\n";
        
        $current_wp_config = str_replace("/* That's all, stop editing", $my_defines . "/* That's all, stop editing", $current_wp_config);       
        file_put_contents(ABSPATH . 'wp-config.php', $current_wp_config);   
    }
}

1. put this to mu-plugins folder.
2. fresh wp install
3. go to admin panel
4. click to tools
5. click to network setup
6. run the setup
7. ???
8. profit!!!