As Admin, I Can't Load My Custom Plugin Functions

My 3rd party plug-ins seem fine. My issue is a custom plugin I am trying to develop (code is below). Long story short, I get the world famous:

“You do not have sufficient permissions to access this page.”

when I try to load the ‘helloworld’ function without using it as a sub menu page. In other words, doing this:

admin.php?page=helloworld

That spits out the permission/access error. Long story short, I need functions to work that are NOT built into the admin menu. The database is not the issue, other plug-ins worked. I am trying to figure out how to fix this since the 1,000 Google searches I did lead to no solution.

Here is the code. TY. I am pulling my hair out.

global $wpdb;
require_once(ABSPATH . 'wp-admin/includes/upgrade.php');
require_once(ABSPATH . 'wp-includes/pluggable.php');

    function fileaccess()
    {
  // basic function that DOES work. I'll spare you the code.
 // All it does is load a directory and display file names inside it.
    }

    function helloworld()
    {
    echo "hello, world";
    }

    function admin_page()
    {
     add_menu_page('test', 'test', 10, __FILE__, 'fileaccess');
    }

# Add Action
add_action('admin_menu', 'admin_page');