I have a UN65KS800DFXZA TV and recently I have not been able to access websites or stream any video. We have a very strong internet connection, about 400mb download. This is only a problem with the Web Browser. We have no issues with the YouTube app, Netflix, Hulu or any other application.
I have no problem using the web browser on the other Samsung TV's in our home which are all further away from the router. We have the same issue whether wireless or wired. I did a full reset of the TV, but this did not change anything, only made have to reload all my stuff.
The firmware is Ver1242 which per the Samsung site is current as of March 02, 2020
The Web browser on my UN65 was always freezing after touching after any search or click of a button. I discovered Facebook Watch which has worked great for any videos inside and outside of Facebook. Give it a shot.