PHP 8.2 Upgrade

I need to upgrade my server to PHP 8.2 or higher, but when I do all my pages disappear. I'm assuming that there are some incompatible coding that prevents these pages from working. Any suggestions on how I should proceed to get up-to-date. I'm currently running PHP 8.1 and everything seems to be working fine.

Hi Bill, add error reporting to the top of a page that isn't loading and let me know what the error message is:

<?php
error_reporting(E_ALL);
ini_set('display_errors','on');
?>

Here is the error and the code of connSiteDB.php

Line 11 is $connSiteDB = mysqli_init();

Fatal error: Uncaught Error: Call to undefined function mysqli_init() in /home/ijj1kpif5p27/public_html/_awlctemplate/Connections/connSiteDB.php:11 Stack trace: #0 /home/ijj1kpif5p27/public_html/_awlctemplate/index.php(5): require_once() #1 {main} thrown in /home/ijj1kpif5p27/public_html/_awlctemplate/Connections/connSiteDB.php on line 11

<?php
# FileName="WADYN_MYSQLI_CONN.htm"
# Type="MYSQL"
# HTTP="true"
$hostname_connSiteDB = "localhost";
$database_connSiteDB = "XXX";
$username_connSiteDB = "XXX";
$password_connSiteDB = "XXX";
@session_start();

$connSiteDB = mysqli_init();
if (defined("MYSQLI_OPT_INT_AND_FLOAT_NATIVE")) $connSiteDB->options(MYSQLI_OPT_INT_AND_FLOAT_NATIVE, TRUE);
$connSiteDB->real_connect($hostname_connSiteDB, $username_connSiteDB, $password_connSiteDB, $database_connSiteDB) or die("Connect Error: " . mysqli_connect_error());

?>