Source

File: wp-includes/sitemaps/class-wp-sitemaps-renderer.php

public function get_sitemap_stylesheet_url() {
		global $wp_rewrite;

		$sitemap_url = home_url( '/wp-sitemap.xsl' );

		if ( ! $wp_rewrite->using_permalinks() ) {
			$sitemap_url = home_url( '/?sitemap-stylesheet=sitemap' );
		}

		/**
		 * Filters the URL for the sitemap stylesheet.
		 *
		 * If a falsey value is returned, no stylesheet will be used and
		 * the "raw" XML of the sitemap will be displayed.
		 *
		 * @since 5.5.0
		 *
		 * @param string $sitemap_url Full URL for the sitemaps XSL file.
		 */
		return apply_filters( 'wp_sitemaps_stylesheet_url', $sitemap_url );
	}