Something else that’s confusing
When cap replaces the stones and decides to stay in the past to grow old, doesn’t the act of him staying in the past create an alternative timeline? (Ancient One and Hulk discussed this and she explicitly made this point)
If so, old man Cap wouldn’t have been able to meet Sam and Bucky in the future since he should be living in another reality
Or was it a time loop and he was always meant to eventually stay in the past and marry Peggy
Yes I brought this up before, Cap appearing at the end raises so many questions.
There's three different consequences to changing the past so far:
1. Taking an infinity stone creates an alternate timeline, one that's 'doomed' according to the ancient one. So the stones have to somehow be returned to the moment they were taken. This doesn't affect the present, but returning them would affect the alternate presents as the timelines are erased.
2. Taking other items, or people, or killing people, must also create an alternate timeline but one that doesn't need whatever was changed or taken to be returned. This also doesn't affect the present.
3. Going back to the past and remaining in the past means you remain in the main timeline and do change the present.
This raises so many questions about everything. Can you travel to the alternate timelines or can you only travel back and forward in the main timeline? For example if they went back to 2015 would Thanos be there or not? What's the present like now that Captain America has been around since the 50s or whenever it was? Can you continually go back and gain infinite infinity stones creating infinite doomed timelines? Why does taking infinity stones doom the timelines but not anything else? If Cap remained in the main timeline, what would happen if for example he caused the death of Howard Stark? Does the timeline only split once something big like that happens? Because Cap would have had to have changed a lot of small things and, given he is Cap, some large things as well. Hence why time travel is too tricky a subject and usually needs one hard and fast rule.
Also how did Stark wield all the stones when it took Thanos and Hulk quite a while to gain control over them and 4 of the guardians to control one.