I'm also having the same problems on my Galaxy s8 (G950FD) on pie since the april security patch, after I updated I instantly noticed some colours were kinda "washed out", colours that were darker became less darkers in system wide/apps, even dark mode was darker in some places before the update, twitch/youtube/instagram/streamings in general are getting pixelated on darkers areas even on the highest qualitys possible, even videos shot with the camera when I watch through the gallery if its darker in any spot is definitely noticiable the pixelating happening, I tried changing up screen modes from adaptive/cinema/basic and such, video enhancer and even resolution didnt made any difference, it was noticiable once I restarted the phone after this april update even that I thought I had did something wrong then searching found this thread and other ones of people with the same problems as mine wish it was reverted to before but doenst seems like its going to happen?
Quicker I can get rid of this phone the better, it's like going back in time 7yrs. The video quality is absolutely awful. Trying to watch videos on Facebook YouTube etc pixelated. Samsung don't care though as long as they get their cash. I've been a loyal Samsung user for yrs but I'm definitely not having another one. Get the latest phone with 7yr old video rendering 😂