Wordpress Sitemaps: disable, remove users, add lastmod

Wordpress 5.5 shipped with sitemaps enabled by default.  This quite possibly isn’t a good thing.

Disable them entirely

add_filter( 'wp_sitemaps_enabled', '__return_false' );

Disable just the Users sitemap

add_filter( 'wp_sitemaps_add_provider', function( $prov, $name ) {
    return 'users' === $name ? false : $prov;
}, 10, 2 );

<lastmod>

If you do want them, you may want to add the last-modified times:

add_filter( 'wp_sitemaps_posts_entry', function( $entry, $post ) {
    $entry['lastmod'] = date( DATE_W3C, strtotime( $post->post_modified_gmt ) );
    return $entry;
}, 10, 2 );