Some would disagree, but if we are talking about mainstream styles from the early 00s it's crucial to speak about the metrossexual moment imo. Say what you want about what they wore, but Beckham and CR7 were very influential, not saying men dressed exactly like them but it influenced the relative power of certain trends. And as I looked into pictures of them, I realize they wore a lot of italian brands! So I would recommend to search pictures of runaway shows from italian brands like Dolce, Versace, Armani, even Prada.
I'm not sure you wanted an essay 😂 but we can start a conversation. It's a cool topic that people still don't talk about that much in the menswear context.
And of course I know there were other styles, trends from that era. I'm just speaking about one of the less niche of them.