Desktop notifications on Macos for Facebook and Twitter will be history, at least a period of time.
Starting with iOS 11, Apple has withdrawn the integration from the operating system of iPhone and iPad for Facebook, Twitter, Flickr and Vimeo. The same thing was done recently on the beta version of Macos Mojave, and most likely this integration of third internet accounts will be missing on the final version.
In the panel Internet Accounts, until Macos Hight Sierra there were separate connection options for Facebook, Twitter, Flikr and Vimeo. With the withdrawal of these accounts, it is unlikely that users can receive notifications through "Notification Center". Most likely Facebook will have to offer a solution in the future.
Most likely these options were eliminated from Apple's desire to store as few private accounts on Macos 11.14 and iOS 12.
Support is still maintained for third-party accounts that offer e-mail services. iCloud, Exchange, Google, Yahoo! and AOL.
