get_author_posts_url( int $author_id, string $author_nicename = '' )

function get_author_posts_url( $author_id, $author_nicename = '' ) {
	global $wp_rewrite;
	$auth_ID = (int) $author_id;
	$link = $wp_rewrite->get_author_permastruct();

	if ( empty($link) ) {
		$file = home_url( '/' );
		$link = $file . '?author=' . $auth_ID;
	} else {
		if ( '' == $author_nicename ) {
			$user = get_userdata($author_id);
			if ( !empty($user->user_nicename) )
				$author_nicename = $user->user_nicename;
		}
		$link = str_replace('%author%', $author_nicename, $link);
		$link = home_url( user_trailingslashit( $link ) );
	}

	/**
	 * Filters the URL to the author's page.
	 *
	 * @since WP-2.1.0
	 *
	 * @param string $link            The URL to the author's page.
	 * @param int    $author_id       The author's id.
	 * @param string $author_nicename The author's nice name.
	 */
	$link = apply_filters( 'author_link', $link, $author_id, $author_nicename );

	return $link;
}