With Manchester United it will be different, the pressure is higher and also Man United is a team that has been slumping for a long time and even for several seasons and some coaches have not been able to meet the expectations of fans and also the targets of Manchester United management.
Ruben Amorim has indeed shown that he is a quality coach with Sporting Lisbon but I doubt that he can do that right away with Man United, maybe he needs more time to adapt to build the Man United team and certainly this is not an easy job for Ruben Amorim.
It takes adaptation and maybe it takes time for any coach to change Manchester United for the better because expecting success in a short time I doubt Ruben Amorim can do it. But usually management will not give a long time and they will demand more expectations from Ruben Amorim to bring Manchester United out of the slump. Even though he was successful at Sporting Lisbon, the English league is very different and maybe he needs to work harder to change the team for the better.
Looking back at Ferguson's journey at Manchester United has similarities with Ruben Amorim and maybe now the story is different because the league is getting more competitive. Give him time to work and we'll see how he can make a big difference from the previous coach.