How to show both first and last name of an user to basic users

Hi every one, 

I'm raising a question similar to this post  [mention:a16c4c9385824e0a9ad9e1c5a4c7ea34:46448885d0e64133bbfbf0cd7b0fd6f7:label=How%20to%20make%20other%20users%26%2339%3B%20profile%20information%20%28e.g.%2C%20first%20name%20and%20last%20name%29%20visible%20to%20a%20basic%20user%20on%20a%20report] as it has not been updated since 6 years ago.

The issue I'm having is for this below code,when opening the UI with a system admin account I can see full user name while with a basic user account I can only see user's first name. 

forEach(local!userNames,
user(fv!item, "firstName") & " " & user(fv!item, "lastName"))

I tried the retrieveusersecurityrolemap() recommended in the old post but not sure what to do with the output of the function, because for both accounts I had the same output:  

Can anyone suggest me how to use this function or any other solution to show the same name for both account types? 

Thank you.