I duplicate courses a lot as so much of the information is the same that it saves time to do this. When a course is duplicated, the assets, such as images, PDF files, videos, and subtitles (VTT) are copied over. I usually replace these assets with different ones.
When you go to the new file manager, the files you have deleted are still showing as associated with the duplicated course. This prevents me deleting files and is very confusing when I want to replace one as I don't know which of the files I should be updating.
I think the correct behaviour for the file manager should be that when you delete an image/thumbnail/video/PDF/VTT file in the course by replacing it with something else, the old one gets disassociated from the course, so that it no longer appears in the file manager attached to that course.
Generally the ability to find files not associated with a lesson and delete them would be great. It is a win-win in that we don't accidentally use outdated files, and Absorb doesn't have an increasing amount of data to manage.