"Opaque" syncing of symbolic links means to sync the link itself, rather than syncing what the link points to. Copying or syncing what the link points to, rather than the link itself is called "transparent" copying or syncing of symlinks.

Transparent treatment of symlinks has been known to be incorrect and dangerous for about 20 years now. Unfortunately, both Dropbox and Insync treat symlinks transparently. In contrast, Unison, "rsync -a" and "cp -R" all do opaque syncing of symlinks, which is the correct behavior for a syncing tool.