For any website, submitting a sitemap to search engines is the fastest way to get your site indexed. Many people have asked what plugins are used to generate sitemap files. In fact, WordPress already has a built-in sitemap function, so there is no need to install any plugins.
The sitemap.xml file submitted by the WordPress site to the search engine was previously generated using the WordPress plugin. in this tutorial, it is introduced how to get the sitemap by plugins, like Rank Math
While actually, the sitemap function has been built in WordPress since the version of 5.5. Therefore now you can just find your sitemap by visiting such a Link https://address/wp-sitemap.xml. For example, I can see my sitemap via this link:https://itodoweb.com/sitemap_index.xml
The wp-sitemap.xml is a summary indexed sitemap file that contains all post_type and taxonomy sitemap files, as well as the sitemap of the current article author.
For efficient file size considerations, WordPress has a maximum of 2000 entries per sitemap file, each of which is suffixed with -n in turn.