Getting a new goalkeeper is not easy and I don't think that any goalkeeper that's in a good club will love to come to Manchester United because it's like they are killing their potentials. Look at De Gea doing pretty good in Fiorentina, that was the best goalkeeper Manchester United had before Ten Hag sold him and brought in Onana. I just hope that all these problems are tackled fast.
If I should say, getting a new goalkeeper shouldn't be Manchester United main priority at this time. They should focus on getting new strikers and defenders. If they should do that, they have solved and covered up to 80% lapses coming from Onana side. And if the team happens to lead by goals in a match, the possibility of the match to end in favor of Manchester United will be there because the team has good forward (strikers) and good defenders.