Also, it’s worth noting that our ancestors have been outside all day every day for millions of years.
It is also probably worth noting that skin color in indigenous populations is extremely correlated with average UV levels in the region, which to me indicates that if you are living in a location other than where your ancestors lived, you can’t really use “our ancestors dealt with this just fine” since it seems the ancestors that didn’t look like the people who evolved in your region failed to breed at much higher rates than the ones who did.
Of course that cuts both ways, since if it were a pure win to be protected from the sun, we would all be dark skinned.
I admit to having missed that footnote, but I think I am intending to make a subtly different point here, which is that not only does a mismatch with ancestral environment undercut the “our ancestors didn’t have sunscreen” argument, but rather the strong correlation between UV intensity and skin color indicates that this is not a weak selection pressure and getting exactly the right amount of sun is probably kind of a big deal.
Especially if it is true that it’s just vitamin D that was imposing pressure towards lighter skin and we can get the same effect that through dietary supplementation.