For those who missed it @bat39 broke down the superman reborn
Doomsday Clock SPOILERS
It just occurred to me that the Metaverse reveal at the end of DDC might finally explain the whole 'two' Supermen situation from Convergence/Superman Reborn.
Here goes-
1. Pre-Flashpoint Superman and Lois exist on Earth 0.
2. Doc Manhattan's tampering alters Earth 0. Pre-Flashpoint Superman and Lois become New 52 Superman and Lois.
3. As a result of Manhattan's tampering, a new parallel earth is created to 'preserve' the Pre-Flashpoint continuity. Pre-FP Superman and Lois continue their lives on this earth.
4. During Convergence, Brainiac grabs the Metropolis from this parallel earth, including Pre-FP Superman and Lois. During their time imprisoned in the bottle city, Jon is conceived and born. Post-Convergence, Pre-FP Superman and Lois end up on Earth 0 and raise Jon there.
5. New 52 Superman and Lois die, and the Pre-FP versions take their place.
6. The essence of the New 52 Superman and Lois 'merge' with the Pre-FP Superman and Lois. This alters the history of Earth 0, restoring its earlier Pre-FP configuration to a large extent.
So basically, the 'split' of Superman into two was caused by Manhattan simply because Manhattan tampering with Earth 0's history caused the creation of a parallel earth that preserved the earlier version of Superman. Pre-FP Superman, despite being from a parallel universe, was essentially a previous timeline version of New 52 Superman - thus he was able to be 're-incorporated' into Earth 0 history, becoming Reborn Superman.