"Os Looks Mais Icônicos de Rihanna no Met Gala Através dos Anos"  

(Alternatively, in a more natural Brazilian Portuguese phrasing: "Os looks mais marcantes de Rihanna no Met Gala ao longo dos anos")  

Both versions are correct—the first is a more direct translation, while the second adapts slightly for flow. The term "looks" is commonly used in Portuguese fashion contexts untranslated, but you could also say "visuais" or "produções" if preferred. "Met Gala" remains the same as it's a proper noun.