I saw your topic here yesterday and remembered a pain of my own, which I already had in exactly the same place with some WordPress projects. So today I spontaneously designed a small plugin that should fulfil exactly your requirement.
As it’s very new, it’s not in the repository or available as a plugin. However, you can download it here: https://github.com/threadi/media-attached-filter – go to Code > Download ZIP and then install the ZIP file in your WordPress. You will then have a new input field labelled ‘Attached to…’ in the Media list view:
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As soon as you search for something in the field, it will suggest a maximum of 10 possible hits in your project. These can be pages or posts. Searches are only carried out in the page title or post title. You must then select the title and can then filter. Only media files that are assigned to the selected page or post should then be displayed.
Does that work for you?
I’m still a little confused that you mentioned folders into which you want to move the files. WordPress does not recognise folders. Are you using a plugin for this, if so, which one? It would be interesting to know in order to test compatibility with it – however, the plugin I created is so minimalistic that there should hardly be any problems.