How to copy/transfer the files/data/posts from production to Staging instance ?
we are working on developing a new theme if we restore a backup from prod instance to staging the developed theme is getting lost.
To test all the functionalities, we would need to import the existing posts from PROD to Staging.
That means there is something wrong with your approach of developing the theme. You need to review your approach and follow best practices for development of themes.
Read: Beginner's guide to developing Discourse Themes
I’ve performed backup/restore across many discourse sites but have never had an instance where design was lost due to backup/restore.