I'm not convinced it's a Samsung issue. Seem more likely YouTube have a problem to fix but I wish Samsung would give some feedback on what they have found out about the problem. I have one 4k film in my library and it breaks up playing via the YouTube app but works perfectly through the Google Play Movies app - both apps on Samsung TV
Article says YouTube only working at 480 but also that tv app should be fine. I've also seen articles about intentional throttling because of heavy use with covid, infection problems at YouTube and Google having their own vp9 encoding system causing issues
I am from Romania (Europe) and I have the same problem with 2 Samsung NU7402 TVs.
I also tried with another router on both 2.4 and 5 Ghz wireless connections and I had the same problem.
When the TV is connected to the internet by cable everything is working fine.
I also tried to watch videos using the Youtube app on a Playstation 4 and everything is working fine on wireless and over the cable.
So I am thinking the problem is with the TV and the Youtube app only when the TV is connected to the internet over WIFI.
I hope Samsung will fix this:)