Although Bellingham is nominally considered a midfielder, he still plays primarily in attack, and in this case Ancelotti will not be able to count on him in the midfield. By the way, there were rumors that Rabiot could continue his career in Real Madrid, but I see that he postponed the decision on this issue after the end of the Euro. He could very well replace Kroos, who retired. And Mbappe, Vinicius and Bellingham will play up front in any case, they are attacking players and it seems to me that there is no point in trying to place any of them in the midfield line.
Ancelotti could really see that Bellingham had quite a high goal-scoring instinct, so he plotted Bellingham to move forward as a number 10 player to cover the central striker crisis that they had so far, What Ancelotti did turned out to be quite effective and was able to make Bellingham being one of the top scorers in last season, currently Mbappe arrival to Madrid has of course forced Ancelotti to re-think strategy and also appropriate positioning for Bellingham next season, as far as we know, Bellingham has his original position as a midfielder but I think He won't play as a midfielder if Ancelotti wants a really dangerous attack line next season.
Currently, Madrid is reportedly continuing to approach several new players to replace the retired Kroos, but it doesn't seem like Rabiot is Madrid's current target, Ancelotti is more interested in bringing in Bruno Guimaraes and Florian Wirtz as another solution for their midfield next season, but I think the need for midfielders is not the most urgent thing for Madrid now, because they still have a lot of young midfielders in their current squad.