In Justice League 39, it is revealed Doomsday Clock happened in a different reality than the current canon.

That would mean Earth-1985, Earth-2 and Earth-52 are not the actual Pre-Crisis Earth-1, Earth-2 and New 52 but rather duplicates because they split off of Metaverse, which is a different reality than the current canon. They would probably be nigh-identical to their main canon incarnations, but they would be seperate.

Also, speaking of current canon, is DC Rebirth the same timeline as Pre-Flashpoint or is it a combination of both New 52 and Pre-Flashpoint (at least currently)?

Is it safe to say when the timeline changes, the universe doean't split off in the current canon (unlike the metaverse)? There are versions of characters from Pre-Flashpoint running around like Superman (I think Pre-Flashpoint Superman is a part of Rebirth version) and Wally IIRC. Ia it safe to say Pre-Flaspoint world is erased?

Also, what happened to the multiverse (including their Earth-2 and Earth-1) in Convergence's Pre-Crisis Multiverse where the COIE is averted?