Resolvi... Era bastante simples 😣
 
	No caso alterei para...
 
	function getPublishedPosts() 
	{ 
	    global $conn; 
	    $sql = "SELECT p.*, u.username FROM posts AS p JOIN users AS u ON p.user_id=u.id WHERE p.published=? ORDER BY `created_at` DESC";
 
	    $stmt = executeQuery($sql, ['published' => 1]); 
	    $records = $stmt->get_result()->fetch_all(MYSQLI_ASSOC); 
	    return $records; 
	}