Hello Maddy,
Hello Maddy there is no specific authorization object for user. That can be done with PFCG menu. You need to play around with the PFCG Role “Menu”. The solution for your scenario is as below:
When I say changes in the menu, I mean changes in the menu tab of the PFCG role assigned to the user. You have to delete the UIU component from the respective folder. In the present case I have taken Sales folder - transaction Opportunity. This holds good for any transaction (eg activities, lead, etc). The moment you delete the link (UIU_COMP link) and save the PFCG Role the authorization tab will become red. Reason being that specific authorization of create/display is deleted. You need to go to authorizations make all green and generate the profile.
You can also refer to the link below, which will be of help to you for better understanding.
Some facts about UIU_COMP authorization object in SAP CRM.
Hope this answer was helpful 
Thanks!
Neha