tgeyer
First, please read the requirements before installing/upgrading. You would've seen that PHP 8.3 is not supported. You need to downgrade to PHP 8.2.
Secondly, you need to check all possible logs (general server logs, webserver error logs, PHP error logs, MySQL/MariaDB error logs, osTicket System Logs, Browser Console logs, etc.) for any related errors.
Cheers.