The Plex app on your TV will not support 10-bit HEVC video, and, by extension, HDR video. Also, if any video needs transcoding, it will be limited to 4 Mbps.
Plex supplies the app to Panasonic, who publishes it in their app store. Any TV can download the app (there may be geographical restrictions). However, unless your model is on the list approved by Panasonic, it will have the limitations mentioned above.
List of supported SmartTVs: Which Smart TV models are supported?
Thread with additional details: 4K (HEVC Main 10 HDR) on QNAP Plex Media Server
If you want to watch HDR video via Plex on your Panasonic, you will need an external streaming device such as an Nvidia Shield, Apple TV, Roku, Amazon FireStick, etc.
