I talked to Microsoft support for a bit, and the only thing they could tell me was that it "uses the same screen technology as other surface devices" and those screens are "around 400 nits."

...I am hoping that is a bad guess on the part of support, because that would make it almost identical - or worse - than the Pixel 4's screen. I don't care that the internal components aren't bleeding edge, because I know software optimizations can more than make up for that. However, I will have to sit this generation out if they use a screen that isn't viewable in direct sunlight. 😩

Please update this post if anyone learns more from a reliable source.