You are not alone in experiencing this bug. I’ve linked the competitive bugs megathread at the bottom of this post, which archives and documents almost every competitive bug. I put your thread under: Missing Top 500 Rewards (Season 4). Please help in spreading the word about this megathread and other related threads, we must demand the Developers to give us the rewards we rightfully earned.
Here’s a thread about your missing Top 500 leaderboard placement issue if you’d like to read more about other potential solutions: The Competitive Bugs Megathread - #318 by Azdyph-1127.
You are correct, the 50 won games requirement was implemented for Role Queue Competitive at the launch of Season 6, so this is not the issue. Unfortunately, Top 500 icons are no longer earnable in Overwatch 2. Link here: Competitive CTF Top 500 icon - #7 by Brigitte-11594. This might have been an issue with the competitive titles, as if I recall correctly, in Season 4, they were updated to differentiate between different competitive gamemodes. However, some players experienced a bug and received the old titles and could not view or equip them. Whatever the case may be, given the seasonal nature of Overwatch 2 competitive rewards, I unfortunately doubt the Devs will award you the rewards you earned. I hope this helped.