I've been reading this thread a lot and I originally agreed with OP, but now I think >>107217190
might actually be correct, he's just explaining it kind of poorly and coming off like a cunt
Describing it as "time bubbles" is just making it more confusing and making it seem like fan fiction, a better way to think about it is when the Avengers go back in time and change things, the Infinity Stones "heal" the timeline once they leave, preserving the future as it was (Hulk is right when he says the future cannot be changed.) Like the Ancient One says, removing a stone disrupts the flow of time and creates a branch in the timeline. When the stones are returned at the end, they "heal" the branches, effectively erasing them.
The reason Thanos and Gamora are not erased by the healing is the same reason the Avengers can take stones or Mjolnir from the past: once something is in the future/present, it cannot be changed. Again, the future/present cannot be changed.
The place where this gets dicey is with old man cap at the end. Seemingly by returning the stones to the timelines and not jumping back, he should have been "healed" out of existence with the branches, which leaves two possibilities:
1. Cap actually DOES jump back to the present timeline, he just waits until he's lived out a whole life with Peggy. The only issue here is why he appears on the bench without his suit or his time gps, but that could possibly be explained away for dramatic effect.
2. It's a closed loop and Cap was always in the past the whole time, and he somehow avoided making any changes so the timeline was never healed/corrected.
I don't really buy #2 because there doesn't seem to be anything else in the film that supports "closed loop" time travel being a thing, but it seems impossible to confirm which is correct until we actually have official word.
Anyway, hopefully that clears things up for anons.