For over a year, Google said it is working with the WordPress team to build in to the core of WordPress the ability to generate XML Sitemaps. Well, now with WordPress 5.5 it is now out. Pascal Birchler from Google announced on WordPress.org “in WordPress 5.5, a new feature is being introduced that adds basic, extensible XML sitemaps functionality into WordPress core.”
With version 5.5 of WordPress your WordPress site will expose a sitemap index at /wp-sitemap.xml. This is the main XML file that contains the listing of all the sitemap pages exposed by a WordPress site, Pascal said. The sitemap index can hold a maximum of 50000 sitemaps, and a single sitemap can hold a maximum of 2000 entries or URLs. All public and publicly queryable post types and taxonomies, as well as for author archives and of course the homepage of the site, will be available in these Sitemap files by default.
For this to work, you need to render the sitemaps on the frontend and that requires the SimpleXML PHP extension.
You can learn a lot more about this over here.
I guess if you have an XML sitemap already on your WordPress site, you can use that and maybe disable this or leave both. I assume plugins like Yoast will handle it and I also think it is fine for Google to consume the same URL more than once in more than one sitemap – although, it is probably not the most efficient way to have things.
Forum discussion at Twitter.