For some reason FinderSync extension can’t be enabled (it’s greyed out) 
It’s mildly annoying as I can’t get a file share link from the browser (it says “permission denied”… 
)
If I remember correctly some versions of macOS and Seafile Sync client work better than others. You might want to consult this post as an example. It also includes some tips on getting the extension running again.
LOL, it just got enabled today after yet another restart of the app 
Umm … did you doing anything other than restart the app?
nope… nothing