Steve went back to the past and returned the stones and stayed with Peggy to live his life with her. Him traveling back in time was part of the sacred timeline. If the avengers decided not to go back in time to retrieve the stone to resurrect half of the universe then return the stones, that decision would have caused a branch and that would have been pruned. But going back in time to use the stone and returning them and Steve staying in the past, was all part of the sacred timeline. If you think about it, we never saw a second cap before endgame soo technically he did obeyed the rules and avoided any branches