Toni Kroos kept his word that he would stop playing football or retire while his game was still at the top and he didn't want to retire when he had to sit more on the bench, and he proved what he said to us now. because currently his game is still very good and he is an option for his club and country, that means that his game is still very good. And if we talk about his current age, then I don't think he is so old to continue playing.
Now even though many fans are sad, as you said they have to respect every decision that Toni Kroos takes to retire as a professional footballer. Even though the club and country still need his contribution, now we can't do anything because he has made his decision. It's not easy to find a player with Kroos' abilities, but I hope that players at Real Madrid and Germany can fill the void left by Kroos.
Don't forget that Hansi Flick and Ancelotti are currently fighting over the same player, namely Joshua Kimmich. Even though I know that Joshua Kimmich's closeness to Hansi Flick is closer, on the other hand, Real Madrid has long term goals for him considering that Ancelotti plans to make Joshua Kimmich a replacement for Tony Kroos. Having both roles as a midfielder and a German player makes Ancelotti want to sign Kimmich, and there are rumors that a deal has been made behind the scenes. If that is true then again and again Real Madrid takes quicker action. In my opinion Madrid offer is much more promising, but we also cannot deny that Hansi Flick offer is an honor for him.