After months of frustration and days of googling (is that a word?) I found this post and tried my luck. I am so happy to confirm this adapter also works on the 2018 models (in my case OLED65C8).
I even took the time to create an account to say thanks. So... THANKS!!!
After plugging in the device it takes some time for the tv to install (I think), after a while I (un)plugged the lan cable again, then the lights started flickering. Still the apps (youtube) say no connection, I had to reboot the tv first. As mentioned by others above, the TV shows no connection for LAN and Wifi, but it all works flawlessly
I downloaded the speedtest app, I get a more then reasonable 250Mbit up/down (I have 1GB up/down fiber connection). So I should be able to play all available 4K videos.
As for LAN content:
I use the onboard LG Videoplayer, it plays almost everything without transcoding over DLNA.
I am able to play all my 4k HDR files right from my synology with Media Server App installed.
Also with Universal Media Server on my HTPC (with some .conf changes) everything plays perfect, incl. subtitles.
Right now I am not at home, but later today I will try and play some of these reference files: http://jell.yfish.us/