I can't think of any use cases for this, could you share? You mean once you get the message and you open it, it gets read (and sender sees that status), but you'd like to mark it as unread again? Why?
I think they called it Inbox Zero back in the days when it was all the hype.
I only open Messages whenever somebody wrote me (which would automatically un-archive the thread).
Telegram supports archiving, and I use it all the time there.