Cooking Tomatoes Boosts Disease-Fighting Power - Cornell University - April 23rd, 2002 was published by a respected university in the USA, and it explains in detail what Hive account@plantstoplanks has described.

There is some much nuance in food chemistry that a yes or no answer can't simply be given, and each individual food must be assessed. Cooking one thing may destroy certain nutrients while boosting the uptake of others, but one clear danger of cooked foods is the heat.

I took a bite of curry fresh off the stove the other day, and that was clearly a mistake because it burnt the roof of my mouth, so there is one example of a negative health effect of cooked food.