As previously mentioned, Thanos has five stones in his possession when he arrives on Earth. One of these is the Soul Stone, which we know takes a sacrifice to get. In the timeline we know, Thanos sacrifices Gamora — quite possibly the only thing he loves — and is one step closer to omnipotent power. However, in this universe, we see that Gamora is still alive after Thanos already has the Soul Stone.
Some fans discussed this very detail in an Episode 8 breakdown on the “What If…?” subreddit. Thanos would have had to sacrifice someone, so who was it? How did he get the Soul Stone? Redditor u/Mhunterjr reminded fans who were confused that this is an entirely different universe, and we can’t assume that anything is the same. “Maybe Thanos yeeted a different kid. Maybe someone other than Thanos acquired the soul stone and Thanos got it from them. This is a completely vastly different universe from the main one, so it makes sense that things behind the scenes played out differently,” they wrote.
In this universe, Thanos may favor Nebula, and maybe she was the one he threw off the cliff on Vormir. He could also have children we’ve never seen. Perhaps the Soul Stone doesn’t even require a sacrifice in this particular reality. We can never assume that anything is the same from universe to universe and timeline to timeline.