Just a few. Enabling it on a few sites doesn't work as expected at all, and the add-on should probably be disabled on those - for example Twitter. First, it tries to enable the dark mode on Twitter, but the tweets itself are all gone (the only thing you see is the heading sections). And when you disable the extension to return to the normal mode, the dark mode remains on tweets (central section) for example, while the rest of it turns white again. That's a bug. I think you might need to crowdsource which websites it doesn't work fine with.
