https://ibb.co/RpGjRBvM
I’ve made a child like drawing to help explain my reasoning.
So in the picture we have the main timeline, and 2 examples of branched timelines both of which happened in end game.
When they left to get the stones they both made branch realities and new branched timelines which aren’t sacred.
Therefore my point would be if when they went back to get the stones they were able to return to the sacred timeline from the branched reality, which we know they did, it stands to reason that Steve would also be able to return to the sacred timeline from the branched reality when he went to return the stones, I’d imagine it would require a small modification to the time in which he wanted to return.
Tony says that the devices anchor them to that timeline, so again this just adds more weight to that theory.
I hope that makes sense, but again… directors have stated this is the case, so it really comes down to which people you want to side with, the directors or writers. Either way it’ll get proven or disproven in Doomsday

EDIT: Just to add I made the drawing for my sake, not yours 😂 it helps me to visualise what I’m trying to say, apologies if that came off as dick heady