Since a user can have a list of roles you can't write an expression to check if a specific user has the administrator role. If there is a certain module role that only an administrator will have you can use the conditional visibility to show the editable field based on this module role.
Or you can check out this widget that determines conditional visibility based on a microflow. You can do a retrieve on the user role table to check for the admin user role with this constraint.
[System.UserRoles = $currentUser]
[Name = 'Administrator']
Edit: conditional visibility is set here
Alternatively, if you set permissions at the entity level (i.e. only administrators can read or write a given attribute), that attribute will not show up on any pages unless the user has the correct roles.
strangely the security settings in System are read-only so I cannot alter the entity security...