yes, you would have to loop through `all` users so that you could then update that user_meta field:  

    // Create the WP_User_Query object
    $wp_user_query = new WP_User_Query(array('role' => 'Subscriber'));
    
    // Get the results
    $users = $wp_user_query->get_results();
    
    // Check for results
    if (!empty($users)) {
        
        // loop trough each author
        foreach ($users as $user)
        {
            // add points meta all the user's data
            add_user_meta( $user->id, 'points', '5', true ); // 5 = number of points existing users will get
        }
 as far as adding this same user_meta to new users you could hook into the login or registration, depending on how you are adding them to the system.  for this you could use `get_current_user_id()` to get the id of that unique user.  

later, you could then just `update_user_meta($user_id,'points');` in whatever function they are earning more points at.

you can find more info on the [WP_User_Query in the Codex][1]


  [1]: https://codex.wordpress.org/Class_Reference/WP_User_Query