The WordPress bug affects websites sitemaps that are generated by the WordPress core. The bug affects websites that have so many pages that they need more than one XML site map. According to the bug ...

* If sitemaps are disabled, only the rewrite rules will be registered * by this method, in order to properly send 404s. * @since 5.5.0 // Add additional action ...

If I visit /wp-sitemap.xml, there is an url in the list: /wp-sitemap-taxonomies-post_tag-1.xml If I click on it, 404 page comes in. All other links are working (like: /wp-sitemap-taxonomies-category-1 ...