@lecorylus Maybe you have enabled the theater mode on YouTube?

I just responded to this question at https://www.reddit.com/r/operabrowser/comments/192weks/youtube_becomes_bright_in_full_screen_regular/ if you want to take a look.

@andrew84 I've been noticing this little blue line on Youbube videos and at first, thought Uh! oh! My Sony 4K TV LCD is breaking down. LOL
I analyzed the issue as related to Lucid mode.

When I saw your post about 110%, I checked my zoom and sure enough, it was at 110%. I put it back to 100% and the line goes away.

Thanks for that tip. I don't have to worry about the TV anymore. LOL

@leoams English here, or post in the appropriate language forum.

@burnout426 battery saver is off. I do have a flag enabled but i tried disabling it but still no use. this problem actually started when i updated opera this week....

In my experience in the past this related to ad blocking, maybe it is in this case, maybe not. I probably won't be back here but thought maybe that you can disable ad blocking or any extensions related to it. Hope it helps but if not, sorry and hope you get it sorted.

Other common suggestions are to clear cache and flush your DNS. These might be helpful as well.

@leocg I figured out the problem myself. My isp is throttling content they don't like.