Up until the "modern era" of Trek, my understanding of canon is that the Eugenics War happened in the 1990s and was immediately followed by WW3. It seems like that has changed.
Picard season 2 took place in the 2020s, and there was no evidence of widespread devastation that would have taken place in a major war, although it could be argued that it wasn't shown to us on-screen. At the end of the series, we see a folder labeled "Project Kahn," hinting that either Kahn has yet to be born or that the season's "bad guy" is planning to continue Kahn's legacy.
In Strange New Worlds Season 2, Episode 3, the focus is on Kahn and how he affects the timeline. We see Kahn as a child, meaning the Eugenics War has yet to take place, even though the episode takes place in what is obviously 2020s or 2030s Toronto. Even more telling is that the Romulan spy says "This should have happened in 1993." Might have been 1992; still, early 1990s.
This leaves me with a few questions. If the Federation time-cops are so set on preserving the timeline, why did they allow the timeline to be altered to such a degree that the Eugenics War, a major event in Humanity's history, happened at least 30 years after it was supposed to. In addition, what event actually altered the timeline so that Kahn was born/created decades later than he should have been? As far as I remember, we haven't seen anything to show why this happened.
Since we now know from SNW that the Eugenics War happened some time after the 2020s, how does that fit into the timeline for Zefram Cochrane's first warp flight? Assuming the Eugenics War is still followed by WW3, that only leaves a max of 49 years between the start of 2 major conflicts and first contact with the Vulcans. In "First Contact," Cochrane and company assumed the Borg attack was from a hostile force on Earth. Perhaps WW3 was still in progress, and the events of 2069 were what ended the war?
On a side note, the destruction of a single ship spawned the Kelvin timeline. Since SNW shows us that events in Earth's history no longer match up with the timeline established in TOS, TNG, VOY, and DS9, does this mean that SNW (and possibly PIC) are also in a non-prime timeline?
This line is a pretty conspicuous breach of the fourth wall placed there by the current stewards of the franchise to tell us that we’re back to pre-Kelvin timeline time travel rules. The whole “time travel creates two discrete timelines” notion is gone. It was a one-off to justify the Kelvin timeline, and now we’re done with it.
It’s all one timeline and while that timeline is in a constant state of flux due to time travelers tinkering with it on a regular basis, it’s still one big wibbly-wobbly timey-wimey timeline. Therefore, the answer to every “are X and Y in the same timeline?” question is a continuously shifting “maybe” which largely depends on how you choose to understand “the timeline.”
To put a finer point on it, this is the writing staff telling the fanbase to chill out about timelines. Akiva Goldsman speaking to CinemaBlend, emphasis mine:
Translation: the Star Trek canon is going to keep shifting forward to accommodate keeping it in our future. More broadly, we should all accept some measure of canon flexibility so Star Trek is always set in an aspirational future, well suited for telling morality tales in space which are relevant to modern issues.
That was how I read it.
Personally I prefer Trek just being it's own timeline with its own history and not treated as part of our future anymore. It's clear we're headed for The Expanse instead of Trek at this point anyway.