Why does rowCount() keeps returning a value of 0 (PDO) in PHP MYSQL

Question

I'm working on a login system, however, I have encountered a problem. How come rowCount() always returns 0. I tried other ways but no luck. I did some research and found out that rowCount() only works with UPDATE, INSERT, AND DELETE, and not with SELECT.

Here's my original code:

       // Verify if password match 
        $hashedPwd = $stmt->fetchAll(PDO::FETCH_ASSOC);
        $checkPwd = password_verify($pwd, $hashedPwd[0]["password"]);

        if($checkPwd === false){
            $stmt = null;
            header("Location: ../login.php?error=incorrect_password");
            exit();
        }
        else if($checkPwd === true){
            // Create prepared statement
            $stmt = $this->connect()->prepare('SELECT * FROM accounts WHERE username = ? AND password = ?;');

            // Execute prepared statement
            if(!$stmt->execute(array($uname, $pwd))){
                $stmt = null;
                header("Location: ../login.php?error=statement_failed");
                exit();
            }

            // Check if username and password exist in the database
            if($stmt->rowCount() === 0){
                $stmt = null;
                header("Location: ../login.php?error=user_not_found2");
                exit();
            }

            $user = $stmt->fetchAll(PDO::FETCH_ASSOC);
            
            // If everything is valid, grab data and assign it to a session and set cookie
            // Start session
            session_start();
            $_SESSION['id'] = $user[0]['id'];
            $_SESSION['username'] = $user[0]['username'];
            $_SESSION['user_type'] = $user[0]['user_type'];
            
            // Set cookie
            setcookie('uname', $uname, time()+60*60*24*30, "/");
        }

I tried using fetchColumn().

       if($checkPwd === false){
            $stmt = null;
            header("Location: ../login.php?error=incorrect_password");
            exit();
        }
        else if($checkPwd === true){
            // Create prepared statement
            $stmt = $this->connect()->prepare('SELECT count(*) FROM accounts WHERE username = ? AND password = ?;');

            // Execute prepared statement
            if(!$stmt->execute(array($uname, $pwd))){
                $stmt = null;
                header("Location: ../login.php?error=statement_failed");
                exit();
            }
             
            $row = $stmt->fetchColumn();

            // Check if username and password exist in the database
            if($row === 0){
                $stmt = null;
                header("Location: ../login.php?error=user_not_found");
                exit();
            }

I also made sure hashed password and user's password is matching and it is returning correct output

    $hashedPwd = $stmt->fetchAll(PDO::FETCH_ASSOC);
    $checkPwd = password_verify($pwd, $hashedPwd[0]["password"]);

    if($checkPwd === false){
        $stmt = null;
        header("Location: ../login.php?error=incorrect_password");
        exit();
    }
    else if($checkPwd === true){
        // Returns true
    }
    else if($checkPwd === false){
      // Returns false
    }
    
    I tried logging in with correct and incorrect credentials and its completely fine.

What am I missing? Could someone please help.