@burnout426 I came across this looking for a solution to the same problem with the checkered pattern appearing briefly on youtube using Opra and this post really helped a lot, this issue wasn't problematic as it was just really irritating not knowing how to fix it and just being a nuisance to me, thanks for the help stranger I could never figure this out on my own, I just had to change my Angle flag to OpenGL as suggested for my Nvidia GPU and it works so far as I can see, no issues anymore! Thank again!

@bigkwii UPDATE:
Disabling the Vulkan flag at opera://flags/ seems to have fixed it.