Hello,

You can do this via Settings / Technical / User interface / Menu items, then in the “Visibility” tab, add for example the “Administration / Settings” group by searching for it in the list. Finally, save and the menu will be visible only to the specified group.

Best regards!

Normaly Odoo Show Apps the user is allowed to use, so if it dont have access to anything than contact, it see only contact.

If you want to have more control over the shown apps to a specific user, I think you will need a custom modules or add access rules in the system parameters.

But having a user access to only one apps make no sense to me, make it a portal user and put your feature in the front end.  It is an ERP with a customizable front end, and erp mean many apps for many users generally