When the world’s greatest and most hated superhero is forced into retirement after yet another fuck up, he searches for his successor via a reality television show where each week contestants battle against villains and each other to prove they can become the next Universal Hero.

Yep, maybe his powers are fading so secretly he is going to use the constant to find someone he can steal their powers off - after all he still wants to be the most powerful hero.

Plus would be good second chance but he learns that you pass on the lessons to the next generation not keep them for your self

Keep with the retiring hero. There is a lot of gold in that:
Can't let go of his glory days
The ?you don't do it that way?
People like the new guy more than him etc

Start with forced into retirement. The other stuff you can show in the action of the Logline.

A bitter superhero forced into retirement uses a reality show to find his successor.

We all know what reality shows look like. So you have space to add some story about his emotional journey.

This should probably be told from the point of view of one of the contestants who is vying for the position of next great?Super Hero.