Casemiro to Manchester United has been completed and an official statement from Real Madrid has come out about it as well. If you told someone this deal could happen a week ago they'd mock you. Completely out of the blue. He is a much needed signing for Manchester United though, solidifying the midfield. I guess that's one way to make Ronaldo feel at home, bring in his old comrade.
Yes, Casemiro's arrival is like an oasis in the desert. Manchester United is one step further helped in midfield. Then the arrival of Casemiro will also have a good impact on United thanks to the wealth of experience he has achieved.
Manchester United's forwards, midfield and defense are all very weak. So I see no reason to think that Casemiro in the team will actually strengthen every position of Manchester United. Casemiro is an experienced player. But in the 2021–22 La Liga season, he scored just one goal and 3 assists in 32 appearances. So I don't think United will be strengthened by Casemiro.