Edit: I was mistaken. I thought the K6500 was pre-Tizen (tech specs).
However, @tom80H is correct. The TV requires an Internet connection to load the app. What is on the TV is a basic bootloader program. Once loaded, it may work without an Internet connection. However, if the app is ever flushed from the TV (power off, etc) it will need an Internet connection to reload it.
I’ve an LG that works the same way. I’ve used the hot-spot on my phone to load the app, then reconnect the TV to my home Wi-Fi. It is a pain, but it worked.
[HowTo] Use Plex with No Internet
Important information about Plex for smart TVs after September 30, 2021
The app was last updated in 2018. There have been many changes to Plex Media Server since then.
Here’s some additional information that may help:
Last version of the app (2018): From the Developers - If there is any news, it’s in here!
Thread mentions proxy to use with older Plex apps: Plex.tv/link not generating code on samsung smart tv
Samsung TV Cannot Connect to Plex
[HowTo] Use Plex with No Internet
Important information about Plex for smart TVs after September 30, 2021
