Google has been working with the WordPress team for over a year to create the possibility of generating XML sitemaps at the core of WordPress. Well, now with WordPress 5.5 it's out now. Pascal Birchler of Google announced on WordPress.org, "WordPress 5.5 introduces a new feature that adds basic, extensible XML sitemap functions to the WordPress core."
With version 5.5 of WordPress, your WordPress site provides a sitemap index at /wp-sitemap.xml. This is the main XML file that contains the list of all sitemap pages exposed by a WordPress site, said Pascal. The sitemap index can contain a maximum of 50000 sitemaps, and a single sitemap can contain a maximum of 2000 entries or URLs. All public and publicly available post types and taxonomies as well as for author archives and of course the homepage of the site are available as standard in these sitemap files.
For this to work, you need to render the sitemaps in the frontend. This requires the SimpleXML PHP extension.
You can learn a lot more about it here.
I think if you already have an XML sitemap on your WordPress site, you can use it and possibly disable it or leave both. I'm assuming plugins like Yoast will handle it, and I also think it's okay for Google to use the same URL more than once in more than one sitemap – although this is probably not the most efficient way to do things to have.
Forum discussion on Twitter.