In football, no. There´s Barcelona and Bilbao in Spain, and that´s about it, at least among the bigger leagues, but let´s leave that.
Of course every club needs to balance the books, but my point is that we have the money to do both, bring in some youth and keep Ronaldo for the 2–3 years that he may have left at the top. There´s been a profit of about 50M euro for about 5 seasons running, and there´s no money outstanding on any past signings. M´Bappé is already more or less budgeted for without having to sell anybody, and the plan is to keep him on loan at Monaco for the next season, precisely for the reasons you offer, so nobody else signs him. Donnarumma won´t cost us a penny in transfer fees, because he´s already informed AC Milan that he´ll let his contract run out next summer and sign for whomever he wants.
Beyond that, Theo Hernández is agreed from Atlético (leftback), and with Lucas Vázquez, Asensio, Mariano, Morata if he stays, Bale whenever he can play, and after that Vinicius when he´s ready, we´re good. I wouldn´t have Lukaku and Mbappé at the same time, it´s a striker overload, and look at what happened this season with Morata, it´s difficult to keep all of them happy if they can´t play.
Also, and going back to money, there´s Ronaldo´s image contracts. Unlike any other club, every player at Real Madrid has to give 50% of his image revenues to the club, as per their contracts. With his Nike contract, and all the other stuff he does, Ronaldo pretty much pays for himself, and no other player in the world we could bring in (operating word here is “could”, Messi doesn´t count) comes even close.