From your post I gather you have a USB drive connected to your Router. That is were your going wrong to use all the lovely UI of Plex. Follow the following instructions to set up your server. Connect your USB drive to your Computer that you have installed Plex Media server.
Prerequisites:
Computer with Server must be on the same Network as your Smart TV.
In your LG app settings/ Manual server/ ( Must point to your server’s LAN IP and Port 32400)
Your storage device/USB Drive to be connected to your Server
Plex Media Server and TV Connected to Internet not using IPv6 in there settings.
As your TV can not Direct Play DTS, it needs to be disabled in the app settings/ Audio/ DTS, DCA
It’s advised to use a Public DNS on your TV, like 1.1.1.1 or 8.8.8.8 instead of your default ISP’s DNS, Manually configure your TV network settings
Were to download Plex Media Server.
https://www.plex.tv/media-server-downloads/#plex-media-server
Guide:
https://support.plex.tv/articles/200264746-quick-start-step-by-step-guides/
Your TV is compliant to the new Preview App
Welcome to Plex
