Hi Laslett,
The Publishing Manager and the ability to use a 3rd party plugin is, at this time, limited to the Lightroom Classic CC product. We are currently looking into ways to publish content to various social sites for future updates to the Lightroom CC desktop product.
With Lightroom CC, all your photos are in the cloud and, by extension, available to all of your mobile devices where they are easily shareable to Instagram and others by using the Share functionality in Lightroom CC for mobile (iOS and Android)
Since, Lightroom CC is a new cloud based Photo editing tool and we are still evolving it. Exporting to Facebook is available in Lightroom. Please add your vote to this discussion by hitting the "Me-too" button up at the top: Lightroom CC: Add publish services (WordPress, 500px, Flickr....) | Photoshop Family Customer Community .This space is being monitored by our Engineering team and helps them in prioritizing product updates and bug fixes.
Regards,
Akash