Barcelona will not sell Lewandowski. Lewa is now almost 37 years old. Even then, he is able to perform brilliantly. We have seen a lot of goals from Lewa this season too. Lewa is Barcelona's top scorer. Barcelona definitely needed Lewandowski in this season.
However, Barcelona will not have the 37-year-old Lewandowski with the squad for a long time. That is why Barcelona will have to try to create a worthy replacement for Lewandowski from this season. With this aim, Barcelona is going to buy Nico Williams. Nico Williams will make a place in Barcelona's main squad in the next few seasons. It is unlikely that Williams will be seen in Barcelona's starting XI this season. Lewandowski, Yamal and Rafinha will be in the starting XI.
Barcelona isn't selling Lewandowski and it's not because of his age, it's because they don't have any choice. They don't have the money to buy player that will be up to Lewandowski standard without breaking the bank. They can get any striker they need but getting upto that Lewandowski qualities will take years of training with experience and that is going to cost them, they don't want to go back where they left where they just pick recently to win Laliga 2 times.
I see players flinch when they get older but it's unusual of Lewandowski to play that way, his touches are still super strong and making 40+ goals isn't something Yamal and Raphina could ever do, maybe someday but with what they have played from the beginning, there is much they can to best men after Lewandowski. He is still representing his national team, hasn't retire and that's because he is fit, and not juts that he is there captain too.