Check out CKEditor 5, with media embed and Markdown support :)

https://ckeditor.com/docs/ckeditor5/latest/features/media-em... Though for Twitter previews you might need to use services like Iframely but there is a ready-to-use integration guide: https://iframely.com/docs/ckeditor

As for Markdown, you can switch the default CKEditor 5 output from HTML to Markdown: https://ckeditor.com/docs/ckeditor5/latest/features/markdown... And Markdown input is provided by a customizable autoformatting feature. It's enabled by default in all CKEditor 5 builds.