Signing Manuel Ugarte is going to help Manchester United and for me, that will be their best signing of the season because the defensive midfield is what Manchester United needs, Manchester united has casemiro and Amrabat who can play the position but those players are too old to hold that position, even their performance throughout last season was somehow poor, signing Ugarte is going to improve the squad, if we look at Manchester United games we will know that is the position they supposed to fight for now, secondly Manchester united also need a goalkeeper because for me Onana is not ready this season.
Man United really needs a defensive midfielder who has the quality to stop opponents' attacks and maybe Ugarte is a good option for Man United. Casemiro and Amrabat are having problems with consistency now because maybe they are talking about age as you mentioned and Man United needs an energetic player who has the ability to penetrate in many ways when facing opponents who are much more concentrated on holding the ball.
Apart from several positions that Erik Ten Hak really needs to improve so that Man United can compete with several other teams. Onana is also not consistent because he often makes mistakes and maybe the coach needs to be firm. Like the previous season and Onana was given too much trust by the coach so he didn't learn from the mistakes he had made.