If Man United looks for a new goalkeeper, there should be 1-2 goalkeepers to be out from Man United because Man United has 3 goalkeepers now. Besides Onana, Man United has Altay Bayındır and Tom Heaton. I don't think Man United will keep all the existing goalkeepers because it will spend too much money for goalkeepers' salaries. As long as they don't break the limit made FFP, I think Man United will have no problem to do it. But honestly, it is too early to buy new goalkeepers because they just signed Onana and Altay Bayındır in the previous transfer window.
Man United has too many problems, they have a problem with defense line and attacking line. I think both defense and attacking deserve to rebuilt. So, I think it is okay if Man United are looking for attackers. But they also need to rebuild the defense line as well.
the issue of disharmony within Man Utd has already been heard quite a bit, before Onana came to Man Utd, Man Utd management reportedly wanted Emiliano Martinez instead of Onana but Ten Hag did not agree with Man Utd management, so actually the recruitment of goalkeepers at Man Utd was influenced due to Ten Hag's decision, in the next transfer season there is a big possibility that Man Utd will hunt for another goalkeeper to accompany Onana, it is also possible that they will continue to target Martinez and 1 or 2 of the existing back-up goalkeepers at Man Utd will be sold to reduce the salary burden.