The next is that the time travel of Thanos and his daughters Nebula and Gamora into the future caused a lot of confusion because they are missing in the past - Thanos was killed, Nebula from the past was killed by Nebula from the future and Gamora simply stayed in the future. How could this happen without having an impact on the future?
As I have already explained in the first part of the time travel theme, it should now be obvious that this is possible, if you start to see time travel with other eyes or if you start to think differently about this topic with Marvel.
Everything that Thanos, Nebula and Gamora have done from the main timeline in their past, they have still done and experienced, i.e. everything that has happened in the MCU so far, everything that we have seen in the movies so far, has not changed, it has all happened that way.
Through time travel into 2014, time and the universe have split and a new timeline and parallel universe has emerged. This means that the Thanos from the past is now a Thanos from another time line and since he died in the main time line, this Thanos no longer exists in the parallel time line. And this also means that the Thanos from the main reality has never travelled through time into the future. All this also means that the Infinity War and the Snap of Thanos also happened, in the main time line, but not in the emerged parallel timeline/universe. There he is dead from that moment on when he travels through time to the main time line, where he is then defeated.
What many also regard as a logic mistake is the reversal of the snap by Professor Hulk. Hulk could have undone everything with his snap, and with everything i mean really all events, the snap of Thanos and even everything before the snap to stop what Thanos intended to do with the Infinity Stones and with that would completly everything undone and even all actions would be impossible in Infinty War and Endgame.
But on Tony Stark's urging this is not done, instead Hulk takes back all beings that had disappeared into thin air five years ago by the Snap of Thanos, without changing anything. There are no changes. What happened in the five years, happened. So everyone came back to the time Hulk did the snap, and not five years back.
This only happened because Tony wanted it so. He did not want to lose his daughter. This zero change is an absolute condition from him. And here it gets interesting again, because here Tony Stark aka Iron Man plays God in a certain way. Now you can decide if the selfless Iron Man wasn't so selfless and acted very selfish instead.
source This graphic explains/shows it best
Part 3 
