It looks like Dropbox will soon stop following symbolic links to files or folders outside of the Dropbox folder.
When placing a symbolic link (symlink or soft link) in the Dropbox folder before this change, the symlink is replaced by the data it points to, so you have the actual data on the Dropbox servers, and not just the symlink.
The "How to use symlinks with Dropbox" page from the Dropbox help mentions that "as of mid-2019, Dropbox no longer follows items outside of your Dropbox account that are linked to by a symlink". I tried both the latest Dropbox beta and stable builds on Linux, and this is not yet the case, i.e. Dropbox continues to follow symbolic links that point to items outside the Dropbox folder.
This change may have already landed on other platforms already, as I only tried the Dropbox Linux client, or it may have been added there in preparation for a future update.