Short Answer: Buy a streaming box/stick - Amazon, Apple, Nvidia, Roku, etc.
Long Answer:
See Which Smart TV Models Are Supported → Devices with Limited Playback Capabilities
No idea why the app is not working.
However, it has limited playback capabilities. It is limited to a maximum of 1080p/H.264 @ 4Mbps video and AAC/FLAC/MP3 2.0 audio. Anything higher will transcode.
Additional details: Plex is always transcoding x265 - #16 by FordGuy61
You would be better served by using a streaming box/stick. Current models from the major manufacturers support 4K HDR video and many more audio codecs.
Here’s a short list of devices that work well with Plex:
- Amazon FireTV Stick 4K Max Gen 2 or Fire Cube Gen 3
- Apple TV 4K
- Nvidia Shield Pro
- Roku Ultra or Streaming Stick 4K
