The one thing I’m still have trouble understanding when it comes to The New 52 to Rebirth transition is the deal with Superman.
So there were 2 Supermen the got merged into 1? How did the Pre-flashpoint Superman survive and stay hidden? Whatever happened to the New 52 Superman? This is the one thing that I still don’t get
Convergence (especially the Superman 2-part tie-in), The Final Days of Superman and Superman: Reborn should answer most, if not all, of your questions
And it’s probably easier to read than to explain!
In New 52, Superman was an unlikable somewhat dark gritty jerk. Then in the event convergence, the pre-flashpoint Superman appeared as a refuge because his universe/multiverse no longer existed. This Superman is married and has a son. When Superman Dies in the Final Days of Superman, the pre-flashpoint superman reveals himself to the world and takes on the mantle of superman. Then in the event Superman: Reborn, Superman syncs himself up with the New 52 timeline, becoming the New 52 Superman and the Pre-Flashpoint Superman in one. Now he is the only superman that’s ever existed.
It still spawns a lot of questions, but that is the gist.