Maybe if you go to flags?
Search for brave://flags/ or chrome://flags and you could something like this:
If you can see there, is an option called Force Dark Mode for Web Contents. Try put it on default or disabled. (I put it on enabled manually and I love it

I hope that work…I mean maybe that extension did this.
Let me know if that solved your problem.
Or that extension has light mode too. Have you tried to reinstall that and switch back to light mode? I only think…I have never installed that enxtension
