It has Ubuntu Linux, I installed a Plex server on it and have a Plex pass subscription for it. I also have one of these

https://www.silicondust.com/hdhomerun/

I have Plex clients for Windows, Mac, Linux, XBOX ONE, PS4 and iOS. I can watch TV and movies on my server or Live TV through the HDHomeRun, or have Plex work as a DVR. I listen to music on my phone with the Plexamp client when I am at work or travelling on foot or in my car. My only complaint is that some files don't play by default on the PS4 and I have to manually tell it to re-encode.

I tried Jellyfin and never got it to really work right. Plex is a consumer electronics-type experience and the Plex Pass is totally worth it.

You can do that with home-built ones. The only thing Synology (or any commercial NAS) actually gets you that you can't get elsewhere is convenience of setup.