@novanightfall It happened to me but I found a solution!
Here are the steps:
Go to Opera GX settings Find Force Dark Pages (You said it didn't work for you but keep reading) Don't click on the On and Off button, click the text itself where it says "Force Dark Pages" it should say "BETA" next to it Click on the 'x'/close button to on the websites under where it says "Enable" to disable the Force Dark Pages for those websites.