Custom auto page reload with js

wpmudev-autoreload-page-content.php

<?php
/*
Plugin Name: Custom auto page reload
Plugin URI: https://premium.wpmudev.org/
Description: It will update the content of the page without member re-loading the page
Version: 2.0
Author: Panos Lyrakis @ WPMUDEV
Author URI: https://premium.wpmudev.org/
License: GPLv2 or later
*/

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

if ( ! class_exists( 'WPMUDEV_Custom_Page_Autoreload' ) ) {

	class WPMUDEV_Custom_Page_Autoreload {

		private static $_instance = null;
		private static $_time_frame = 5; //seconds
		private static $_content_wrap_element = '.entry-content';

		public static function get_instance() {

			if( is_null( self::$_instance ) ){
				self::$_instance = new WPMUDEV_Custom_Page_Autoreload();
			}

			return self::$_instance;

		}
		private function __construct() {

			add_action( 'wp_footer', array( $this, 'load_script' ) );

		}


		public function load_script(){

			global $post;

			if( ! $post instanceof WP_Post || ! apply_filters( 'wpmudev_allow_autoreload_page', true, $post ) ){
				return;
			}

			$rest_url =  esc_url_raw( rest_url() ) . 'wp/v2/posts/' . $post->ID;

			?>
			<script type="text/javascript">
				(function($){
					$(document).ready(function(){
						var time_frame = 1000 * parseInt( "<?php echo absint( self::$_time_frame ); ?>" ),
							last_modified = "<?php echo $post->post_modified; ?>",
							rest_url = "<?php echo $rest_url; ?>";

						/*var Base64={_keyStr:"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=",encode:function(e){var t="";var n,r,i,s,o,u,a;var f=0;e=Base64._utf8_encode(e);while(f<e.length){n=e.charCodeAt(f++);r=e.charCodeAt(f++);i=e.charCodeAt(f++);s=n>>2;o=(n&3)<<4|r>>4;u=(r&15)<<2|i>>6;a=i&63;if(isNaN(r)){u=a=64}else if(isNaN(i)){a=64}t=t+this._keyStr.charAt(s)+this._keyStr.charAt(o)+this._keyStr.charAt(u)+this._keyStr.charAt(a)}return t},decode:function(e){var t="";var n,r,i;var s,o,u,a;var f=0;e=e.replace(/[^A-Za-z0-9\+\/\=]/g,"");while(f<e.length){s=this._keyStr.indexOf(e.charAt(f++));o=this._keyStr.indexOf(e.charAt(f++));u=this._keyStr.indexOf(e.charAt(f++));a=this._keyStr.indexOf(e.charAt(f++));n=s<<2|o>>4;r=(o&15)<<4|u>>2;i=(u&3)<<6|a;t=t+String.fromCharCode(n);if(u!=64){t=t+String.fromCharCode(r)}if(a!=64){t=t+String.fromCharCode(i)}}t=Base64._utf8_decode(t);return t},_utf8_encode:function(e){e=e.replace(/\r\n/g,"\n");var t="";for(var n=0;n<e.length;n++){var r=e.charCodeAt(n);if(r<128){t+=String.fromCharCode(r)}else if(r>127&&r<2048){t+=String.fromCharCode(r>>6|192);t+=String.fromCharCode(r&63|128)}else{t+=String.fromCharCode(r>>12|224);t+=String.fromCharCode(r>>6&63|128);t+=String.fromCharCode(r&63|128)}}return t},_utf8_decode:function(e){var t="";var n=0;var r=c1=c2=0;while(n<e.length){r=e.charCodeAt(n);if(r<128){t+=String.fromCharCode(r);n++}else if(r>191&&r<224){c2=e.charCodeAt(n+1);t+=String.fromCharCode((r&31)<<6|c2&63);n+=2}else{c2=e.charCodeAt(n+1);c3=e.charCodeAt(n+2);t+=String.fromCharCode((r&15)<<12|(c2&63)<<6|c3&63);n+=3}}return t}};*/

						setInterval(function(){
						
							$.ajax({
							    url: rest_url,
							    method: 'GET',
							    //crossDomain: true,
							    //beforeSend: function ( xhr ) {
							    //    xhr.setRequestHeader( 'Authorization', 'Basic ' + Base64.encode( 'wp_username:wp_password' ) );
							    //},
							    success: function( data, txtStatus, xhr ) {

							        var d1 = new Date( last_modified ),
							        	d2 = new Date( data.modified ),
							        	timeDiff = Math.abs( d2.getTime() - d1.getTime() ) / 1000; //seconds

							        if( timeDiff > 0 ){
							        	last_modified = data.modified;
							        	$( '<?php echo self::$_content_wrap_element; ?>' ).html( data.content.rendered );
										wpmudev_notify_content_reload();
							        }

							    }
							});


						}, time_frame );
					});

					function wpmudev_notify_content_reload(){

						popup_wrap = $( '<div/>',{
							"class":"wpmudev_notify_content_wrap",
						} );
						

						popup_content = $( '<div/>');
						popup_content.css( { "padding":"20px", "text-align":"center", "color":"#eee" } ).html( '<?php _e( "Page content has been updated" ) ?>' );

						popup_wrap.append( popup_content );

						popup_wrap.css( { "background":"rgba( 0,0,0,.7 )", "border":"2px solid #C5B358", "border-radius":"15px", "position":"fixed", "z-index":"9999" } );
						popup_wrap.css("top", Math.max(0, (($(window).height() - popup_wrap.outerHeight()) / 2) ) + "px");
					    popup_wrap.css("left", Math.max(0, (($(window).width() - popup_wrap.outerWidth()) / 2) + $(window).scrollLeft()) + "px");
					    popup_wrap.on( 'click', function(){
					    	$( this ).fadeOut( 3500 );
					    } );

					    setInterval(function(){
					    	popup_wrap.fadeOut( 3500 );
					    },'6500');

					    $( 'body' ).append( popup_wrap );

					}

				})(jQuery);
			</script>
			<?php

		}

	}

	add_action( 'plugins_loaded', function(){
		$GLOBALS['WPMUDEV_Custom_Page_Autoreload'] = WPMUDEV_Custom_Page_Autoreload::get_instance();
	});
}


/*
add_action( 'rest_api_init', function() {
    register_rest_route( 'api/v2', '/post/(?<id>\d+)', array (
        'methods'  => 'GET',
        'callback' => 'get_post_content',
    ) );
} );

function get_post_content( WP_REST_Request $request ) {

    $post = get_post( absint( $request->get_param( 'id' ) ) );

    if ( ! $post ) {
        return 'Invalid ID';
    }

    return apply_filters( 'the_content', $post->post_content );
}
*/

You'll need to change line
private static $_content_wrap_element = '.entry-content';
so it contains the class or id of the element your theme uses to wrap post content

You may also like to change how often to check for updates by changing line
private static $_time_frame = 7; //seconds