Question
The required application is no longer available in the Plesk application catalog for installation after updates in December 2018. Why?
Answer
Since the former APS catalog isn't maintained by CloudBlue (Ingram Micro) anymore, Plesk has switched the source of the application catalog to its own.
As an alternative, install Softaculous Auto Installer extension offered in Plesk Extension Catalog, and install applications from there.
Note: This extension is available for Linux Only.