I have 2TB of Dropbox for my Photo Albums (and have had for many years).
All folders were synchronised to my laptop but a mix of online and offline.
My laptop has circa 1TB free.
Last month Dropbox updated the Dropbox App and all files were removed from my PC.
I have added the Dropbox app back to my machine and there is not room to add all of my files.
Using selective sync I can add files to my HDD but when I set them to online only to free up disc space they continue to exist on my HDD. The white tick on solid green background turns to a green tick on white background (like they are online only) but they are still on my HDD.
If I use the 'Manage hard drive space' the app will allow me to select the files and allow me to make them online only. The dark blue area of the used space bar reduces and I get the message; "All offline files were successfully moved to online-only, Nice!" But no hard drive space is freed.
If you run 'Manage hard drive space' again the offline files are all back.
You can make them offline repeatedly but when checking they are still there - even though the icon is green tick on white background (so they should be online).
If you go into airplane mode the online only files are still on my HDD.
I know I am not the only person having this problem. I have seen lots of people with similar problems and I cannot see any satisfactory explanation / solution.