If Trent Alexander-Arnold does join Real Madrid this summer, fair play to him. I was once tempted to make a big move to Spain myself.
Alexander-Arnold is 26 and out of contract at the end of the season, so he is in a position where he either commits the rest of his career to Liverpool or decides to go to Real - who clearly want him.
If he was to leave Liverpool for any other club you might wonder why, but, because it is Real we are talking about, I don't think you could question it as a career move.