What you want is a laptop with a matte screen. Not a "glossy treated for reflection/matte like", which is what you find on most expensive laptops like those from Apple, but actually matte.
It's kind of hard to find because it doesn't sell well because the colors are very much toned down on it, but you can have the sun right behind your screen and it won't matter. I still have one from ~2012 (from the french store LDLC, which are rebranded custome made Clevo) that I gave my GF, and for work purpose and always being at top visibility the screen destroys anything else I've used since.
I'm genuinely weirded out that as far as I know there is no major work brand like XPS or MBP offering true matte screen as options anymore ...
PS: if you haven't seen one before, it's truly no reflection/competition with the sun at all, and it's truly washed out colors.
EDIT: I would at least like to know why I'm downvoted ? A true matte screen is vastly better when facing sunlight, which is what I'm answering to
I love my custom ordered 2010 Macbook Pro with matte screen. It's a shame they took the option away with the Retina models. All I really want is for someone to make that same machine, but with up-to-date components.
It looks just fine and plenty bright, although it is clearly far worse looking than your regular glossy screen (since that's their perfect conditions). So in that scenario I would prefer a glossy screen because the colors are better BUT I would have no problem with a fully matte one.
And then in a fully dark room, I would again say the matte it superior to glossy because it's brightness feels much less abrasive to the eyes (but my eyes tend to be sensitive to light, I'm the kind of person who needs to change his screen luminosity depending on condition, so for people who don't care about that it would be glossy being better due to the colors I guess)
I recommend using polarised sunglasses. The macbook screen is polarised the correct way for most sunglasses, so it doesn't dim your screen half as much as it does your surroundings.
My iPhone pushes up to 725 and it's useable with sunglasses at the beach.
Discontinued Lenovos OLEDs had pissy 330 cd/m2...