So I have a headcanon, and I desperately need somebody to write it in a fanfic. Or maybe it already exists and you know such a ff?? ? Give the link in the comment, please.
So:
Tony and Steve notice at "The Winter Soldier" stage that something is wrong with the Shield and that maybe Hydra is interfering with it.
Overall, Tony knows Steve is looking for Barnes because he secretly helps him. Because this is the beginning of their romantic relationship.
And by the time it gets to the scene where Ross introduces them to the Accords and tells them to sign, they will agree that they will pretend to be on opposite sides to trick Ross and Hydra. To make them think Tony is on their side, so that he would have access to their information.
A fight in Siberia could happen, because maybe Bucky switched to Winter Soldier mode (thanks to Zemo) and Steve couldn't stop him and it wasn't Steve who was fighting Tony, but Bucky.
Tony talked T'Challa into taking Rogers, Barnes and Wilson to Wakanda and hiding them there.
And he was contacting his sister about fixing Buck's arm.
And of course Steve and Tony meet in secret all this time.
Tony works to defeat Hydra and clear Rogers and Barnes of the charges (because he discovered that the footage of the night his parents died is a photomontage, it wasn't Bucky).
Did I mention Tony and Steve are in loooove?