I just watched the movie today because i wanted to view it when the crowd is little and there are little noise from other movie-goers. I apologise first if there is already a general concensus of how the timeline(s) play out.

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My opinion is that he definitely created a new branch in the timeline that is NOT the MCU (aka our) timeline we see in the movies. The timeline he inserted himself into definitely has another Steve Rogers, except it wasn't made known to us viewers what happened to this timeline's Steve Rogers or whether Peggy knew the Steve she was with was actually 2019 Steve.

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I personally think that the Steve we saw on the bench at the end was 2019 Steve living in the past, counting time and waiting till the moment he was supposed to "return" from returning the stones (reliant on him actually surviving that long), then used the Pym particles to come back to his original (our) timeline to pass on the torch. What the movie didn't show was probably him returning to his new life, given that they are now able to synthesize more Pym particles and old Steve would have no problem doing so (previously before Hulk undid the damage they mentioned there was no more Pym particles, but after Hank returned i believe they could produce more).