Another criticism is that the oldman cap can't end up sitting on the bench if they only travel in parallel realities. Now that depends. As far as is clear, Cap travels at the end into the year 1940, approximately shortly after the event where he crashes into the ice with the bomber, in his first film. What also confused many is that many think Cap has to reappear on the platform, but the time travel from 2012 to 1970 proves that he doesn't really need this platform.
The only thing that is important are the Pym-particles. And in every timeline he travels to, there exists Hank Pym, the inventor of this particle, i.e. he could find Hank in every timeline and get even more Pym particles. This is all speculation from me of course but the directors have also made a statement on this subject.
They explain that Cap is taking this away and creating a parallel reality in which there are two Captain America, one in the ice and one marrying Peggy. This old one travels back to the main timeline one last time at the end of everything and hands Sam the new shield. And this is really a completely new shield, which doesn't show any signs of use and looks a bit different than we know it. This means that Cap lived happily in the past of a parallel timeline and made up for what he missed.
The Russo brothers say that this parallel reality would be a very exciting future story within the MCU, in which Cap nevertheless appears as Captain America in the 40s, 50s and later, which could be an interesting indication of what is still planned.
But exciting is also the fact that the snap of Hulk has brought back half of the universe to 2023 and not to 2018, when Thanos made the snap. This created a new complex world, because here live people who have mourned for five years and now the disappeared people are back for whom no time has passed. I think this new world also offers many new interesting possibilities. Twins who now have an age difference of five years or people who have remarried or parents who now have five years older children, such as Scott Lang aka Ant-Man etc and so on.
But also possibilities for Hawkeye and his story have been deposited here. In those five years he slaughtered every criminal he could get in his fingers. What about the criminals the snap brought back? Thanks to Hawkeye, they have virtually no rivals. Or what happened to Loki who disappeared in 2012 because Tony Stark and Steve Rogers ruined the plan when they tried to get the Tessarakt?
These are all open questions and their answers are not given to us. Well, not yet. In addition to this complex new world, five new timelines and parallel universes/realities have emerged. And these are only the ones we now have in the MCU so far we know. Maybe even more exist? Everything is a lot of stuff for something new and maybe soon the Marvel Cinematic Universe will be renamed into the Marvel Cinematic Multiverse?
source This graphic, created by a fan, explains/shows time travel in the MCU best
