That's a huge issue that I can't just copy-paste text with formatting (Rich Text) in Joplin – it looks just as where I copied it from at first, but after I reload the note, it's just pure text without formatting.
I googled and find just in the first place the open-source tool that can Convert Rich Text to Markdown and it works very well! Can you please embed it in Joplin?
I try to avoid the Markdown editor because I imported Evernote enex-files which are like html. My notes are therefore html and not well readable but contain all the formatting. In the background it is still Markdown as I understand it but with extensions.
When I copy text with the Rich Text Editor I have to make sure that the target note is also in html. You can check if the note is in Markdown or html by clicking on the i-button (or on Note Properties).
It is mentioned that the issue with enex notes will be addressed in one of the upcoming updates. Just informing you.