Five different covers, and the main characters in this issue aren't on any of them?

...did they have the title and the release slot, then had to write it?

I think I'm confusing Dark Crisis with Death Metal Trinity Crisis, mostly just because I bought them from the same dollar bins. This issue I can recommend, though! From 2023, Dark Crisis: Big Bang #1, written by Mark Waid, pencils by Dan Jurgens, inks by Norm Rapmund.

The opening is pretty stark, as the Flash--Barry Allen--stares at a hologram of the multiverse and announces "I'm looking for the man who murdered me." He explains to Kid Flash (Wallace) and the reader, that the "cosmic limitation" on the multiverse had been lifted (from 52, presumably) and now an infinite number of earths were there to be rediscovered. But, that also could mean the Anti-Monitor was out there destroying realities, and the Flashes head out in search of him. They zip through several universes, a neat little tour, before finding the Anti-Monitor hitting Earth-28, a mech-suit version of the JLA. Barry had just wanted to do recon, but when Wallace is grabbed he has to pull out one of his more dangerous tricks: run repeatedly around the world, accelerating to nearly-infinite mass, for a punch that knocks the Anti-Monitor across realities!

Barry keeps that up, repeatedly hitting Anti-Monitor and avenging his torture on the treadmill in the original Crisis; but A-M eventually grabs him. (The above page isn't just neat; it's also thematically appropriate, since Batman and the Joker were among the last to see Barry alive in Crisis!) It's all over for Barry, until Wallace shows up, with back-up gathered from all over the multiverse! Barry briefs them on the plan, to knock the Anti-Monitor into the anti-matter universe; but doesn't tell them that whoever lands the last punch to shove him in will probably get sucked in as well. Racing around the world again, his life passes before his eyes in an instant, but he's okay with it, and knocks the Anti-Monitor through...but is himself saved by the Batman Green Lantern! (I think that's from Batman: In Darkest Knight, although I can't remember if he had the bat-ears in that one!) I really like the ending, though, where Barry describes the multiverse as "a door to a place without limits." (Or, it can be like everyone you know, only as pirates or cowboys or dinosaurs or...) 

This is perhaps not unlike that Spider-Boy issue we saw a while back, that also walked back the destruction of some minor yet beloved alternates. Also this issue, after a tribute to Carlos Pacheco; Barry Allen's notes on the multiverse and the earths he had cataloged: Kamandi is back on Earth-51, Tommy Tomorrow on Earth-54, and I wonder if I can find a reprint or cheap copy of Adventure Comics #387. The cover doesn't mention it, but Earth-387 is described as "no divergences in history other than every inhabitant is a werewolf." Sounds fun!