I don't think Inter would accept 40 Million Euros to let Onana leave them because Inter is currently in similar situation like Manchester United where they don't have other good goalkeeper which can replace their main goalkeeper. Inter do have Samir Handanovic, but he's already old and can only play for few matches.
Inter will demand crazy amount money to Manchester United, it's better for Manchester United is looking a new goalkeeper in Championship league or other league 1 clubs.
The negotiation between MU and intermilan is still ongoing now for onana. Onana's transfer will be complete very soon. As far as i know that if intermilan gave an ultimatum for manchester united to complete onana's transfer this week.
Intermilan will not accept further negotiation till sunday of this week. Mu must be moving as soon as possible to complete the transfer before sunday.
It's caused by intermilan feels MU was making the transfer becomes even more complicated. It's still possible to add additional budget for the club to buy onana from intermilan.
MU has not yet agreed with chelsea to buy mason mount from chelsea and it's still having a lot of fresh money to be used to buy onana. I think that the deal between onana and manchester united will be reached as soon as possible.