This marks another example of the river of time being diverted, but ultimately leading to the same destination. Miles Dyson, the main person responsible for Skynet’s creation in the future, sacrificed himself in Terminator 2 to blow up the headquarters of Cyberdyne Systems, which had housed the damaged CPU and right arm of the T-800 from The Terminator. With Dyson dead, those components later being destroyed and Sarah lowering the benevolent T2 T-800 into a vat of molten steel, surely that was enough to avert the apocalypse, right?
Article source: https://www.cinemablend.com/news/2481646/terminator-dark-fates-skynet-replacement-has-been-revealed