Does my LG TV SJ800V have a network problem?

I own a LG webOS TV SJ800V. For a few weeks now I've been downright desperate.

Now to my problem: Usually the TV is connected directly to the router (Speedport smart 3) with a LAN cable. This has actually always worked, but for a few weeks it has unfortunately been the case that shortly after I switched on the TV and wanted to watch Netflix, Disney + or similar, the wired connection (Ethernet) is lost. Shortly afterwards it is back. Then again not. And so it goes on.

I've already plugged the cable into other ports and swapped the cable with others several times.

The whole thing wouldn't be so wild now, because you can actually connect it via Wi-Fi. Unfortunately, the TV tells me it can't find a router. Neither mine nor those of the neighbors. (WLAN is of course also possible with other devices, my IP receivers that are connected via Ethernet all work.

So I guess it's the TV somewhere. Has anyone had any experience with something like that?

I have already reset the factory settings, also placed the router in a different place and checked various settings (of course, I may have overlooked something)

Have already gone through countless forums and read about Wi-Fi card exchange, etc. But at least my ethernet would have to go.

If it can help: my Magic remote control sometimes works very poorly. It very often "stalls" and loses the signal, although you can see from the red light above that it is trying to communicate. (Batteries already exchanged and reassigned, of course)

Is this only the case on tv, the internet gone and back again?

or also on the pc?

if also on the pc then it is on the router!

As mentioned above, all other devices work fine.