really bad resolution

Hi there...
Ever since the current league started, my graphic resolution is crap. It feels like playing a game from the year 2000 and it sucks all the fun out of the game :(
When the league started, I read something about ggg having disabled HDR or something, but it hasn't improved since then. I asked around, someone told me I needed to change my port to NAT type "open", but that didn't change a thing. Then I was told my internet connection was simply too slow, but a friend's connection is much slower and he doesn't have the problem. I have a wired connection of course, every TV and xbox (series s) setting seems to be in order. Can anyone pleaaase tell me if there is any way to fix this? Or do I just have to live with it?