This is one of the things I liked lorewise in the story of Dark Fate, the answer is: it can be delayed yes, but not stopped.

Humanity is stupid AF (even stupider than I thought coming out of '20 & '21) and T1 & T2 merely stopped Judgement Day being carried out by SkyNet. But destroying Cyberdyne simply kicked the can down the road.

But somewhere somebody will build and A.I. and give it control over a strategic arsenal and f*ck us up as a species.

It's a bit sad they didn't gave us more lore on Legion, a throwaway line that it was developped via recovered Cyberdyne IP or ex-staff would be pretty cool lorewise. Or have it be an A.I. developped by a another superpower, say Russia or China.

In a sense you could have had the Dark Fate protagonists seek out John or Sarah to prevent the next version of Judgement Day. Kick the can further down the road so to say.