Both Real Madrid and Chelsea seem to have no serious intention to sign Benzema. There is no big advantage to have him in the squad. Benzema even failed to play well in Saudi, how can expect him to play well in Europe? Real Madrid focuses to sign young strikers, their targets are Mbappe and Osimhen. Meanwhile Chelsea already have Nicolas Jackson. Chelsea also prefers to sign young strikers.
The era of Benzema was over, he is no longer in the prime age. Why he must return to Europe now?

He played in Europe and conquered Europe last season so I don’t understand what you mean by Benzema can’t play in Europe. It’s not even up to a year that he left and you are already criticizing him, we all know what Benzema is capable of and even if he is back in Europe he will still be able to perform well.
Real Madrid should rather focus on signing Mbappe than bringing Benzema back, Mbappe will suit them better and will bring lots of opportunities to the club.
Chelsea signing Benzema will not be a bad idea but they should go for a younger player like Osimhen rather than Benzema because of the age difference. Benzema would also be nice option though if they fail to sign Osimhen.
Benzema is a very good player but it's common practice for Real Madrid to get rid of old players and that's a very good tactic, it's the best to invest in young players and when you have a coach like Ancelotti, it's not difficult to make well-playing team and build a new, high value players. I think that Mbappe will be the best player to buy for Real Madrid but it's not the financially wise decision. For the current Real Madrid team, financially Osimhen might be a very good option but his is very injury prone player. Mbappe is the best stable long-term player but he will drain their budget. I think that Haaland will be the best option for them.