At the time of this writing, the Plex Media Server package available in the Package Center of Synology DSM 7 operating system is still in Beta. The Plex Media Server package available in the Package Center app of your Synology NAS is officially supported by Synology. Installing Plex Media Server from the Synology Package Center:

Initial Configuration of Plex Media Server.Configuring Shared Folder Access Permissions for Plex Media Server.Manually Installing the Latest Version of Plex Media Server.Installing Plex Media Server from the Synology Package Center.I will show you how to use Plex Media Server as well. I will also show you how to download the latest version of the Plex Media Server package for the Synology DSM 7 operating system from the official website of Plex and install it on the NAS. This article will show you how to install Plex Media Server on the Synology DSM 7 operating system from the Package Center app. Plex can organize video and audio files as well. Plex can stream movies, music, TV shows, LIVE TV channels, and so on from the Plex server.

Installing plex on synology