Hey
@HoaL, welcome to our Community!
It does seem like you enabled the computer backup feature and your desktop files are now backed up to Dropbox.
You won't be able to remove the app data folder though, without
uninstalling the Dropbox application. Is that what you want to do?
If it is, you'll need to
disable computer backup first and move your desktop files back to their original locations.
Let me know if you have any questions!