@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.