Real Madrid needs a good player to replace Modric and Kroos. Every team knows that and they will try to prevent Madrid from having a good midfielder or simply increase the price of the specific positions that Real Madrid are thirsty for.
I doubt PSG will sacrifice any of its good player because it has a good squad, they might add more players, sell those who aren't that useful but certainly will not allow these useful and having a contract for more than a year.
I don't agree with the idea that Real still haven't managed to replace Kroos. They have Valverde, and in my opinion, he's no worse. As for Modrić, yes, he's an important player, but if you look at last season, he often came off the bench, which shows he can no longer play a full match at the same level. He simply doesn't have the stamina for it anymore. So I think Alonso could move Bellingham into midfield as an attacking player, and in my opinion, that would be a pretty good decision. At the same time, it would open up a spot up front for Mbappé, who has returned to action after his injury.