keunk
Your images/attachments shouldn’t have been touched by the upgrader at all so you probably overwrote those files/folders or something when uploading the new code. If you don’t have a backup of the original files then you might have lost them.
As far as the 500 error you probably didn’t upgrade PHP to 8.0 or 8.1 before trying to visit the site (with the updated files). 500 is a generic error and is indicative of a deeper issue that should be logged in one of your log files (general server logs, webserver error logs, PHP error logs, MySQL/MariaDB error logs, osTicket System Logs, Browser Console logs, etc.).
Cheers.