Issue: If styleConfig: headingStyle = 'linebreak' || 'hashify', header elements are not getting processed i.e elements remains as it is.
Content used: https://developer.mozilla.org/en-US/docs/Learn/Getting_started_with_the_web/JavaScript_basics
Code: htmlToPlainText(plainText.html(), {headingStyle: 'linebreak'});
Reason I found: The corresponding regular expressions are not matching the header elements.