Pixelated Netflix quality? Blame TV or Netflix?

For some time now I have a Hisense Smart TV (H55BE7000 - 55 inches - 4K Ultra HD). With total euphoria, I immediately installed all channels and all streaming services. Of course, this also includes Netflix. Unfortunately, my joy was short-lived. When I registered and started the new season of YOU, the picture was sharp, but green, purple and white pixels / spots flickered on the entire screen. Of course, I couldn't start my series marathon that way.

Then, of course, I checked with the other streaming services to see if there was the same problem. But with Maxdome, AmazonPrime and YouTube there were no problems. I thought maybe it was because I was upgrading my Netflix account because it was a 4K Ultra HD TV. But again, no improvement, the pixels / stains remain.

There were no problems with isolated series (such as Elite). I devoured this series today and then I wanted to watch Love is Blind and these pixels reappeared.

I have already contacted Netflix, who put the problem on Hisense. They in turn want me to reinstall Netflix or send me some (quote) "manual software update" by email, which I then have to install via USB stick.

Since this sounds quite complex, I wanted to ask if someone already had such a problem and if and how he / she solved it. It would be so great to finally be able to watch Netflix again.

Thank you for your answers.

P.S.: Of course I have already tried to set the TV to the factory settings, I have already unplugged it, tried different picture modes and checked the internet connection, just for your information.

I only found the following things.

Internet connection of 25 Mbit / s should be available (https://help.netflix.com/de/node/306)
some internet providers do better than others (https://ispspeedindex.netflix.com/country/germany/)
https://help.netflix.com/...&q=Hisense

I don't have my own experience with it, unfortunately