Thanks for getting back to me. I wasn't expecting a response. As you've mentioned below it is now off which is great. It was just a very jarring, personally I feel its best to allow users to make their own opinions of the experience, I don't find the dark mode experience that bad at all. The text is white and the background is black. Good enough for me!

You seriously have to ask? Pop-up blockers were invented for a reason. Things that jump out and demand your attention are annoying, period.

Thank you for your feedback. I have removed the pop-up for now. No warning about the ugly readability experience in dark mode.

if you really care about it, can already detect it, and show a pop-up, surely it'd also be doable to show a header or something?

as others have said, the pop-up is really the issue here.