Matthijs de Ligt is a talented enough player. And he is a good defender for a big and renowned team like Bayern Munich. Bayern Munich's defense needed to be strengthened. If de Ligt can adapt well to the Munich team, Bayern Munich's defense will be stronger next season. The important thing is that de Ligt's fitness is excellent. At the same time, this young player will be able to stay with Bayern Munich for a long time
I am not sure if he is fast enough though. I mean he is definitely a great defender at an "anchor" role if you want him to play like that. But at the same time we are talking about a player that may not fit the tactic of Bayern.
Usually the defenders there are very fast, and they are very big and strong at the same time, which means that we are going to end up with a player that would a bit shine out of everyone else. Would it work? Maybe, I do not know, I am not a great manager or something, I am just a guy who talks about football and watches football, and a bit wagers on football. But if nagelsmann wants him, and they get him, then they probably have a system in place in their minds.