Hello,
Thanks for contacing us. I hope you are doing well.
It is not possible to restrict user/agent to specific category but there is a workaround.
You can allow agent to view ticket which are only assign to them, here if you are using free version then you need to manually assign the ticket to the agents. If you are interested automated process of assigning the ticket based on the condition then please visit this link to know more about the premium add-on.
You can find the agent role capabilities at Support > Support Agents > Agent Role. While there is no way to restrict users to create tickets in specific category.
Thank you.
