It is very simple method, we have 2 options in Drupal 8.
https://www.drupal.org/project/simple_sitemap
1. we can add by config page of module like (//localhost//admin/config/search/simplesitemap/custom). There add custom links with priority with change frequency.
2. we can use alter method with simple steps::
a. Create any custom module or write code in any existing custom module.
b. go to custom_module.module file or create new if not exist.
c. write code line with below given example:
Example:
First render class library in file header.
use Drupal\simple_sitemap\Simplesitemap;
/**
* Use this hook to add arbitrary links to the sitemap.
*
* @param array &$arbitrary_links
*/
function finder_simple_sitemap_arbitrary_links_alter(&$arbitrary_links) {
// Add an arbitrary link.
$arbitrary_links = array([
'url' => 'https://localhost/applications',
'priority' => '0.9',
'lastmod' => '2020-05-25T14:40:30+02:00',
'changefreq' => 'daily',
],
[
'url' => 'https://localhost/products',
'priority' => '0.7',
'lastmod' => '2020-07-15T13:40:30+02:00',
'changefreq' => 'daily',
],
);
}
Note: We can't add date(lastmod) in custom links by admin, so we have to use alter code for add dates(lastmod) in custom create links.
Note: If have any suggestions or issue regarding 'How to alter or add custom url links in simple sitemap in drupal 8?' then you can ask by comments.