Kroos' absence could impact Real's midfield if Ancelotti fails to find a good replacement for him. It will be very difficult to do this fully, because he was a player of a very high level, but in time Ancelotti will cope with this task, perhaps Rabiot will take his place if he decides to leave Juventus, at the moment he has not decided anything with the extension of the contract, he left the solution to this issue after the Euro, I think everything should be resolved in the near future.
Finding a replacement like Kroos is very difficult because he has matured so much as a midfielder. But Ancelotti must find a solution so that Real Madrid remains strong and has players who are able to maintain the rhythm of the game in midfield.Rabiot might be an option but there is no clarity regarding that so Real Madrid must try to find some suitable replacement figures.
They also have several young players who might be able to replace Kroos' role, but their skills and composure will definitely be different because their experience is not yet as mature as he is.
Madrid's main weakness next season will be not having two experienced midfielders like Modrich and Toni Kroos in the team at the same time. Modrich and Kross are two of the best midfielders of the moment. Even though I'm not a Madrid fan, I'd say there are no more experienced and talented midfielders like Modrich and Kross in La Liga. And finding suitable replacements for these two midfielders is not possible for Ancelotti at the moment. But Ancelotti will definitely keep Madrid's overall performance stable with his excellent match strategy.
Bellingham is a very talented young midfielder. Last season he scored a lot of goals and assists in a Madrid jersey. If Bellingham can continue his form and fitness then Madrid's midfield will be stable next season. But Ancelotti has several young talented midfielders at his disposal. Tchouameni, Camavinga, Arda Guler and Valverde are all very talented. With the help of Ancelotti, if these players become experienced, Madrid's midfield will be even stronger.