The Zend Framework 2 is utilized by the Magento 2.3.x editions. Due to its refusal to use Zend Framework 1, certain functions are implemented differently than in prior iterations (ZF1).
The ability to send emails with attachments is one such feature. Adding attachments to emails was simple in earlier versions of Magento 2 thanks to the function createAttachment().
Use the shared code to add an attachment with Email Magento 2.3.x if you are using the upgraded versions (I'm sure you care about security enough to use the most recent Magento 2.3.2).
Visit : https://meetanshi.com/blog/add-attachments-with-email-in-magento-2-3-x/