Question about the ending of Endgame

When Endgame ended, Captain America went back in time to return the Infinity Stones to their original places to not cause any horrific alternate realities.

But after returning them, he decided to stay in the past with Peggy. He grew old in the past like he originally was supposed to (if he didn’t go in the ice) and then as an old man gave the shield to Sam Wilson.

But after finishing Encore I have questions about that whole sequence. Loki comes to his and Peggie’s home to tell them he can help them. The main theory is that he will move them to a different universe to let them live peacefully without causing incursions or something like that. Even if he doesn’t do that and Steve stays in the original timeline, does that mean that we know that he survives whatever Doom has planned and will, at one point, give the shield to Sam?

Or is it just much more complicated? Will Loki move them both to the future? Is it part of another timeline? Will the original Endgame ending even exist after the events of Doomsday or not?

Sorry if this is obvious and a dumb question, I’m just trying to wrap my head around the whole thing. Right now that just doesn’t make sense to me. If there isn’nt a concrete answer to my questions, what are your guys’ theories?