If you like eating your cauliflower roasted, then go for it. Food should be enjoyable so if you don’t like raw cauliflower and prefer roasted, do that. Even if some of the anthocyanins break down, you’ll still get plenty of other benefits from the fact that you’re eating vegetables. If you’re eating other purple and blue foods, you‘ll be getting anthocyanins from other parts of your diet as well. As long as your diet is colourful and varied and you eat things you enjoy, that’s great, and I wouldn’t overthink it too much on any given nutrient. Plus cooking actually makes some nutrients more bioavailable (e.g. vitamin A). Big picture: eat your veggies however you like. Hope that answers your question :)P.S. I’m a registered dietitian and work in eating disorders/disordered eating/intuitive eating