I have one site where the share feature is available:

The other sites do not seem to have it available.

I followed the guide and ensured all user groups, but "Guest" have been given permission to each of the following:

I can't seem to find a setting (that jumps out to me) that would turn sharing on or off.  Not sure why one site it would work and other sites it doesn't.

 

 

I believe the sharing links only show in forums that are accessible by guests. If you need to log in to see a forum, the share links won't be visible (as most services will just return a 404).