I recently turned on an old computer that was linked to my Dropbox. When I did, all the old files that hadn't been synced in a long time from that computer's Dropbox ended up adding to my current Dropbox, rather than the current version just updating the old computer. Is there a way to make all the old files disappear again without having to go through hundreds of files deleting all of the old things?
Based on your description, it looks like there may have been a computer running the older version of the Dropbox application that had not been connected or updated in some time so when this computer was connected, it added files or folders that were in that computer's Dropbox folder but that were missing online as though they were new files, rather than deleting them from that computer to match the website.
If you'd like assistance with reversing these unwanted additions (you should be able to delete any unwanted files if needed), let me know and I'll reach out to your Dropbox associated email address so I can then forward your request to our Restorations team.