Develop a new widget using the theme function with the Elementor page builder plugin.

functions.php

//Elementor Function Code
class ElementorCustomElement
{
	private static $instance = null;
	public static function get_instance()
	{
		if (!self::$instance)
			self::$instance = new self;
		return self::$instance;
	}

	public function init()
	{
		add_action('elementor/widgets/widgets_registered', array($this, 'widgets_registered'));
	}

	public function widgets_registered()
	{
      // We check if the Elementor plugin has been installed / activated.
		if (defined('ELEMENTOR_PATH') && class_exists('Elementor\Widget_Base')) {
 
         // We look for any theme overrides for this custom Elementor element.
         // If no theme overrides are found we use the default one in this plugin.

			$widget_file = get_template_directory() . '/lib/widget_name.php';
			$template_file = locate_template($widget_file);
			if (!$template_file || !is_readable($template_file)) {
				$template_file = get_template_directory() . '/lib/widget_name.php';
			}
			if ($template_file && is_readable($template_file)) {
				require_once $template_file;
			}
		}
	}
}
ElementorCustomElement::get_instance()->init();

widget_name.php

<?php
namespace Elementor;
class test_widget extends Widget_Base{
	
	/** Get widget name */
	public function get_name(){
		return "widget name";
	}
	/** Get widget title */
	public function get_title(){
		return "widget title";
	}
	/** Get widget icon */
	public function get_icon() { 
		return "fa fa-list";
	}
	/** Get widget categories */
	public function get_categories() {
		return [ 'general' ];
	}
	
	/** Register widget controls */
	protected function _register_controls() {
		
		//Content
		$this->start_controls_section(
			'content_section',
			[
				'label' => __( 'Content', 'plugin-name' ),
				'tab' => \Elementor\Controls_Manager::TAB_CONTENT,
			]
		);
		
		//Description
		$this->add_control(
			'item_description',
			[
				'label' => __( 'Description', 'plugin-domain' ),
				'type' => \Elementor\Controls_Manager::TEXTAREA,
				'rows' => 10,
				'default' => __( 'Default description', 'plugin-domain' ),
				'placeholder' => __( 'Type your description here', 'plugin-domain' ),
			]
		);
	
		//end control		
		$this->end_controls_section();
	}
	 
	/** Render widget output on the frontend */	
	protected function render() {
		$settings = $this->get_settings_for_display();
		//echo item description
		echo '<p>' . $settings['item_description'] . '</p>';
	} 
	
	/** Content Template widget output on the frontend */	
	protected function _content_template() {
		//echo item description instantly on any change value
		?>
		<p>{{{ settings.item_description }}}</p>
		<?php
	} 

}
Plugin::instance()->widgets_manager->register_widget_type( new test_widget);