Hi @Simon,
That is definitely not an issue with osTicket or with osTicket Awesome, or else I would have received hundreds of urgent reports by now!
HTTP Error 500 is a generic message. The real error message isn’t displayed to the visitor for security reasons. The real error message will be in your Apache logs.
But the first thing I would try would be to downgrade PHP to 7.3. osTicket does not support 7.4 yet.
Let me know if that resolves the issue for you.