I have a requirement to hide all users except the currently logged in user for t

I don't believe there is any way to accomplish that on a per-login basis with the OOTB User Record. You can modify the security of user accounts (Modify User Security node), so users cannot see each other (which would accomplish this), however they will not be able to find other users in pickers, etc. One option just for the User Record is to display a dynamic List View - it is not clean and will show blank placeholders for all other records, but I don't believe there are many ways to accomplish your requirement. You could combine this with a facet that returns "Me" or something of the sort, for finding your own user record item, but again it's not pretty.

if(rf!username = user(loggedinuser(),"username"),
rule!USER_LIST_VIEW(),
{}
)

Alternatively, you could create your own service-backed User Record and shut down the OOTB Record, but I do not believe that is recommended.

Per the documentation, forum.appian.com/.../User_Profile_Visibility.html , "If a user is not visible, his User record will not be accessible."