Definitely if there is an offer for him he will consider it very well but the consideration wouldn't be if Manchester United will be losing money from him because high offers come from quality and when there is no quality higher offer will be reduced to the length the players is and is obvious there wouldn't be high offer for him because already clubs who are considering of replacement of goalkeepers are not much because keepers are not always the problem but for Onana is a big one, so actually if there is a big offer Manchester United coach wouldn't think twice.
Refusing to sign a new contract with David De Gea, letting him go as a free agent, and buying Onana is one of biggest mistakes on transfer market and player resource management in Manchester United recent years. They tried to change and believed in Solskajer and Ten Hag but at their goalkeeper position, they actually made big mistake.
Onana with many matches for Manchester United, and with enough given time and patience for showing his ability, is an undeniable failure for Manchester United. They must improve their squad this summer starting with Onana as a good goalkeeper can contribute like 50% of a squad power by great saves that worth similarly to goals.
If they don't improve quality of their backline from goalkeeper to defender positions, their squad will continue to be very weak and vulnerable to opponent attacks and have high risk of losing many matches as well as dropping many points.