ffGetUsersList.php

<?php

/**
 * WP USER LIST
 */
add_filter('fluenform_rendering_field_data_select', function ($data, $form) {

    if ($form->id != 7) {
        return $data;
    }

    // check if the name attriibute is 'dynamic_dropdown'
    if (\FluentForm\Framework\Helpers\ArrayHelper::get($data, 'attributes.name') != 'dropdown') {
        return $data;
    }
	
	/*
	USERS RULES IN WP
		administrator
		editor
		author
		contributor
		subscriber
	*/
	
	//Getting all user inside this $userArray
    $userArray=[];
	
	//Calling the users inside this $allUsers
	$allUsers=get_users('role=administrator');
	
	//Looping them and creating the dropdown option
	foreach($allUsers as $user){
		$siteUsers=[
            "label"      => $user->display_name,
            "value"      => $user->display_name,
            "calc_value" => ""
        ];
		//Now put the users inside this $userArray
		$userArray[]=$siteUsers;
	}
	
    // Lastly returnig the data in the fornend
    $data['settings']['advanced_options'] =$userArray;
    return $data;
}, 10, 2);