I'm currently not using any javascript bundler or preprocessor and I use the ckeeditor build from CDN:
<script src="https://cdnjs.cloudflare.com/ajax/libs/ckeditor5/29.2.0/ckeditor.min.js" integrity="sha512-wwT0JJH+SBiBr/tGqYtpnYLSMOpDt3fLdY1XHWyGSN7YWPnmdz/CoSYUa+ystmwqnb07QvtslyRjciQ9uIhVkg==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
ClassicEditor.create(document.getElementById('myeditor'))
How do I add markdown plugin?
https://ckeditor.com/docs/ckeditor5/latest/api/module_markdown-gfm_markdown-Markdown.html