How to add metaboxes to your plugin settings page

<?php
/**
 * Plugin Name: Metaboxes on Plugin Setings Pages
 * Description: How to add metaboxes to your plugin settings page
 * Version:     1.0
 * Author:      malCure
 * Author URI:  https://malcure.com/
 * Text Domain: malcure
 * License:     MIT
 * License URI: https://opensource.org/licenses/MIT
 * Plugin URI:  https://malcure.com/
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly
}

final class my_metaboxes_init {
	static function get_instance() {
		static $instance = null;
		if ( is_null( $instance ) ) {
			$instance = new self();
			$instance->init();
		}
			return $instance;
	}

	private function __construct() {
	}

	function init() {
		add_action( 'admin_menu', array( $this, 'settings_menu' ) );
		add_action( 'load-toplevel_page_malcure', array( $this, 'load_meta_boxes' ) );
		add_action( 'load-toplevel_page_malcure', array( $this, 'add_meta_boxes' ) );
		add_action( 'load-toplevel_page_malcure', array( $this, 'add_admin_scripts' ) );
	}

	function settings_menu() {
		add_menu_page( 'My Plugin Settings', 'My Plugin Settings', 'manage_options', 'malcure', array( $this, 'settings_page' ), 'dashicons-chart-pie', 79 );
	}

	function load_meta_boxes() {
		add_action( 'add_meta_boxes', array( $this, 'my_plugin_metaboxes' ) );
	}

	function add_meta_boxes() {
		do_action( 'add_meta_boxes', 'toplevel_page_malcure', '' );
	}

	function add_admin_scripts() {
		wp_enqueue_script( 'jquery' );
		wp_enqueue_script( 'common' );
		wp_enqueue_script( 'wp-lists' );
		wp_enqueue_script( 'postbox' );
	}

	function settings_page() {
		?>
		<div class="wrap">
		<h1 id="page_title">My Settings Page Heading</h1>
			<div id="poststuff">
				<div class="metabox-holder columns-2" id="post-body">
					<div class="postbox-container" id="post-body-content">
						<?php do_meta_boxes( 'toplevel_page_malcure', 'main', null ); ?>
					</div>
					<!-- #postbox-container -->
					<div id="postbox-container-1" class="postbox-container">
						<?php
								do_meta_boxes( 'toplevel_page_malcure', 'side', null );
						?>
					</div>
				</div>
			</div>
		</div>
		<script type="text/javascript">
		//<![CDATA[
		jQuery(document).ready(function($) {
			// close postboxes that should be closed
			$('.if-js-closed').removeClass('if-js-closed').addClass('closed');
			// postboxes setup
			postboxes.add_postbox_toggles('toplevel_page_malcure');
		});
		//]]>
		</script>
		<?php
	}

	function my_plugin_metaboxes() {
		add_meta_box( 'my_first_metabox', 'My First Metabox', array( $this, 'my_first_metabox_html' ), 'toplevel_page_malcure', 'main', 'high' );
		add_meta_box( 'my_second_metabox', 'My Second Metabox', array( $this, 'my_second_metabox_html' ), 'toplevel_page_malcure', 'side', 'high' );
	}

	function my_first_metabox_html() {
		?>
		Howdy! I'm your first custom metabox. Now with some WordPress and PHP magic you can customize me as you like.
		<?php
	}

	function my_second_metabox_html() {
		?>
		Meanwhile, I'll sit in the side. I'm your second custom metabox.
		<?php
	}

}


function my_metaboxes_init() {
	return my_metaboxes_init::get_instance();
}

my_metaboxes_init();