It is a profitable business from free agents to be able to sell 50/55 million if this scenario occurs, while Inter Milan can buy a goalkeeper at a lower price but of course you are right it will not be easy for Inter to find a goalkeeper of Onana's class anymore because already have extraordinary abilities.
I think Inter Milan is currently considering it, if for example Inter is ready to let go then the negotiations from Manchester United won't take long because Erik Ten Hag still wants goalkeeper Onana to be included in their project plans with Manchester United.
The great profit doesn't get them very far. As ajiz138 pointed out correctly, it will not be easy for Inter Milan to find a goalkeeper of the same class.
Goalkeepers in general are hard to be found when they really want one who belongs to the top 10 or even top 5 in the world. I would say that even a top 10 goalkeeper is not available right now and if one was available, it would cost more than 50 million. I think it started with Alisson Becker that transfer fees for goalkeepers also went up and are now closer to 100 million than they are to 50 million.
But if Inter Milans wants to attack again in all competitions they have no choice but to find a goalkeeper of the same level.
True it is hard to find but they are still goalkeepers at a good level that hasn't been in much targeted yet by the clubs like Livakovic. Take the situation of Mendy until he was approached by Saudi club. Mendy was bought below 20m Euro and Livakovic also is having interest but none at the level of Inter with around 7m Euro bid. Yes, it is bit hard to find but if they have good scouts then I think they really can find themselves a good buy. I hardly see much competition between the clubs when it comes to buying a goalkeeper as compared to players at other positions.
This was obviously a good deal for Liverpool. Liverpool actually needed a good midfielder. It was good to see that they were able to finalise this deal without making too much noise. I am quite sure that if they actually waited long enough, they would have actually missed out on this player. Because once a player is making some noise in the transfer market he is for sure going to be approached by other clubs and he is going to actually get a good offer from other clubs which will probably end up making him turn away from the initial offer that he got. And I know that he is not a proper midfielder. But that makes it more interesting because Liverpool will be able to use him as a winger and also an attacking midfielder as well.
He is more like a winger basically. Right winger is confirmed Mo Salah for Liverpool so I am expecting Szoboszlai to play at left wing most of time for Liverpool next season. Could be mid also like you said as they are kinda low in terms of depth at mid at the moment with lot of players leaving and age getting some of them. Anyway, it is a good signing and I am looking forward to see how Klopp uses him in the squad.