Benzema is indeed a record scorer at Real Madrid but currently Benzema often does not fully contribute to Real Madrid due to the injury he has experienced, while at Real Madrid no one can replace Benzema's position, therefore Real Madrid must buy another new player who has expertise such as that possessed by Benzema to replace Benzema when he could not participate in the field.
Benzema belongs to top scorers in Real Madrid history but the past season is likely his best season for Real Madrid. He is very old already and even the past season, his performance is very surprising. I knew Benzema is a very good player since his young time in Lyon and many years in Real Madrid. But having a past season at his age is unbelievable.
However, after that he has problems with his body that is normal for old players and I don't think he will be able to repeat another amazing season like the past one.
Even if Benzema can recover, Benzema is possible to get injured again. You must know that Benzema already got injured several times so far, it is proof that he isn't in the best condition this season. Real Madrid can't rely on Benzema, they need a new striker to keep the strength of their attacking line. Real Madrid only has Benzema who plays well as a center forward, there is no other player who can replace his role in the current Real Madrid squad.
Strikers from a same generation of Benzema like Cavani, Suarez, Ibrahimovic and Cristiano Ronaldo started to have problems with body, more injuries, less playing matches or decreasing performance. Benzema is not an exception, if it is not this season, next one, it should come very soon.
Real Madrid know about this fact and they are trying to replace Benzema with Mbappe but failed in the last summer. Who will be a next striker they will aim at after Mbappe? Haaland already joined Manchester City in the past summer too.