It already explain in the movie, the future which is the current one we watch would not be changed. A change in the past would just create another timeline, thats why captain return back the stone. So when Thanos from 2014 come to the future, it created another timeline where thanos cease to exist.

make sense but that will lead to another question which is;
if Capt stay in that timeline after he return the stone, it was not possible for him to grow old and connect to the present time line.
because the past that he stay will branch out and create another timeline that is without thanos.

Physicist theorized time travel came in 2 forms. Single loop that adhere to grandfather's paradox. Infinite loop that has endless parallel realities. Any changes in timeline will just branch off another reality. Comicbooks gave it a fancy name called Multiverse. Like what was demonstrated on Rick and Morty, Looper, Fringe, etc... To make it "idiot proof" you focus on the timeline that matters narratively otherwise it's a slippery slope to tell a story out of it.

The bigger issue I had is stealing gemstones from different timelines does not create nuclear butterfly effects. "Primer" demonstrated how difficult it is not to sets off butterfly effect. They oversimplified it by returning the stones to respective timelines. The million dollar question is the act of snapping, does it erase Thanos from an all encompassing existence or only in the Endgame instance or maybe I wasn't paying enough attention when Hulk mansplaining it to Ancient One. If they only wipe Thanos from Endgame timeline meaning events post GOTG1 will take a different path that has nothing to do with Thanos influence. That's an alternate reality already.

Moral of the story is there's no simple way to do a time travel storyline without butchering factual time displacement depiction.

This confusing me as well, because its connected to present timeline

Yeah...that Loki created another timeline which I'm guessing is a setup to the tv series.

The part where banner explains to the ancient one. Esp how the/if the stones were taken, creates another and how they plan to return it

Time travel has lots of theories, non of course are proven. It’s just an accepted theory

The part where Ancient One said "without the stone, the universe will go to a dark path" is interesting considering the main timeline lost all the stones.

But maybe Bucky already knew or Cap already told him his plans before he went back to the past. There's a Falcon and Winter Soldier series coming.

Bittersweet feeling. The future avengers will never be the same without Steve Rogers & Tony Stark. Why marvel? Why?

Everyone seems to be questioning the part how Thanos transport himself and his army through, if you miss out.

There was a scene where Nebula gave Thanos a cylinder of Pym particles