Anyways, I've thought about this some this month. Now that my mind is less tense and more clear-headed.
I think most of the character arcs in the DCEU are completed. Besides Darkseid (who resides outside of any numbered universe) and Mr Mind's "7 Realms" obsession. Not even counting Lex and Deathstroke, because the new scene they filmed for the Snyder Cut in 2021 was implicitly to resolve that as "it was never going to work out for Slade in the end."
The Mr Mind thing I hope carries over somehow, plus the linger threat of Darkseid seems far more likely for the distant future of the DCU.
But I'm now open to separating the timelines after Aquaman 2. It's clear to me now that they don't have to build off anything that is reaching or has reached its proper conclusion. And the comics did introduce something that could contribute an idea to how The Flash's ending scene matters as it's own bubble away from the DCU:
dc.fandom.com
The Snyder Films (with Clooney replacing Batfleck in the timeline), Ezra's Flash and Momoa's Aquaman exist on a different, undesignated Earth now via a "4th dimensional Earth swapping"; but Blue Beetle and Peacemaker are now on this new Earth-1 born after Flashpoint's undoing.