I tried looking up "broiler" but couldn't pin down exactly what tool you're referring to. I don't know about you, but I don't usually go over a lasagna with a blow torch just to make it look pretty 😄 Even less so a leftover lasagna that I'll be eating on my own.
it should be way less black anyway. Alot of people won't eat that for health reasons when it looks like that
My point was that it isn't black. It's not charcoal you're looking at there, but a deep brown.
It's not that I prefer it to look like that, but that this just happens when you put lasagna in an oven unless you're meticulously monitoring the temperature/radiation and setting the timer just right so that you catch it before it starts forming bubbles (I usually put an aluminum sheet on top when it's had enough color). That said, I've seen lasagna from brick oven restaurants a lot more "severely burned" — and I'm not even selling this one! Though the problem is compounded when using actual lasagna sheets unless you shatter the top layer (I used cooked spaghetti in this one).
Regarding those pictures they look like crème brûlée, which is a bit of a stretch comparison since I'm not going to be sprinkling sugar on top of a lasagna.
Maybe I'm wrong about the caramelization as the only source of the brown color — my main point was that it was brown, not black

Caramelization of the lactose is the one thing I know will give that color, but I could be proven wrong, and that it's actually the flour going brown. I just looked it up: the other reasonable candidate would then be "Maillard browning".
Seems like a bit of a stretch to view that 0.2 mm layer as particularly unhealthy though if this same process happens whenever you're baking an ordinary loaf of bread 🤷♂️
I fully admit to being lazy and imprecise when cooking lasagna now after having done it a hundred times 😩