The opening scenes of Terminator: Dark Fate retroactively reveal that in addition to sending the advanced prototype T-1000 back in time to 1994 Skynet also sent a handful of T-800's back in time after 1994 as 'slow bullets' in case the T-1000 failed. One of these T-800's tracks down Sarah and John Connor at a beach bar in Livingston, Guatemala, killing John Connor. However, because of the death of Dr. Miles Bennett Dyson and the destruction of his work at the Cyberdyne Systems laboratory Sarah and John Connor also successfully averted Skynet's development and stopped Judgment Day.
Yet it is revealed that in Skynet's absence another artificial intelligence called Legion was developed to combat Cyberwarfare and when it inevitably became self-aware it resulted in a new Judgment Day and a subsequent future war with humans fighting against Legion's army of Terminators and H-K's (Hunter-Killers).
As covered in Time Travel Explained, through this narrative Terminator: Dark Fate implies that two futures have existed. While looking at the narrative of Terminator: Dark Fate from the perspective of its present-day setting the possibility of multiple futures is entirely viable, however, the ramifications of extreme changes to any one of those futures would through causality create paradoxes that would result in the events that have already transpired to have never happened. For example if Skynet never existed then no Terminators were sent back in time to 1984 and 1994 meaning the events of the first two movies never happened, and by extension, the events of Terminator: Dark Fate cannot happen.
"There is no fate, but what we make"
