Laravel Mails Swift_IoException Unable to open file for reading

There is a similar question here: "Unable to open file for reading" (Swift_IoException) in Laravel Mailable

However the accepted answer doesn't solve my problem. I also saw the documentation for attachments

I am trying to attach file while sending mail and here is my code.

 public function build()
    {
        $folder = public_path('/email');
        //Get a list of all of the file names in the folder.
        $files = glob($folder . '/*');
        //dd($files[]);
        
        
        if (!empty($files)) {
            return $this->subject($this->subject)->markdown('mail.newsletter')->with('data', $this->data)->attach(public_path('/email') . $files[0]);
        }else{
            return $this->subject($this->subject)->markdown('mail.newsletter')->with('data', $this->data);
        }
    }

I get this error while program enters into if condition.

Swift_IoException Unable to open file for reading [/home/riwaj/Desktop/Project/Library/public/email/home/riwaj/Desktop/Project/Library/public/email/attachment.jpg]