You can enable the "Private" mode for individual forums, users will only be able to view and reply to their own threads. Administrators, or any other group of your choice, are able to see all threads and answer them, including all features that regular threads have. You can learn more about this feature in this product spotlight: Private Forums, Modification Notices and Custom Forum Icons.
Please be advised that this feature is not a full-fleged ticket system, for example, there is no automated ticket status nor does it support replying to these "tickets" via email.
If you're looking for a dedicated ticket system that integrates into our software suite, then please have a look at this paid plugin:
WoltLab Cloud
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WoltLab Suite: Ticket System
An comfortable ticket system for reporting support tickets and software bugs.