Lewandowski is still the best striker, but he is old. In my opinion, it is better for Barcelona to sell him because he still has high value because by selling Lewandowski, Barcelona has the capital to buy other players. Moreover, currently Barcelona is still having financial difficulties buying new players to strengthen the squad next season.
In fact, there are several players in Barcelona's main squad who still have high selling value, perhaps one of them is Frenkie de Jong. He also had to be sold because he had been at Barcelona for five years and had not made a big impact at Barcelona. Maybe this is what Xavi has to do so that Barcelona continues to move forward, by selling several players and bringing in new players because they cannot just rely on young players like Vitor Roque and Marc Guiu. Thus, I am sure that next season Barcelona will be able to compete in Laliga and the UCL League.
At this age of Lewandowski, no team in Europe will consider buying with a high amount of money. Lewandowski was bought from Bayern Munich with a fee of €45M, which team did you think could even pay €30M for Lewandowski at this age? Although he's a good striker, despite that he is 35 years old now. Lewandowski's contribution to the club this season was not that bad as a striker, he scored 18 goals in La Liga and scored 3 in the Champions League. Barcelona has been having financial difficulties since 2022, they don't have enough money to sign a young strike, I believe that is why they went to sign Lewandowski at the age of 33. Except for any team from Saudi Arabia that wants to buy him.
If Barcelona want to compete in La Liga next season, they need to sign more players, they don't have to rely on their current players because they can't achieve much with them. Since Barcelona bought De Jong, I have not seen any of his contributions to the club, he's currently out of their squad due to an ankle injury, I don't even remember when last he played for Barcelona because he usually picks up injuries. If Barcelona did not have enough money to sign top players, the best option is to sell any of their current players who did not contribute to the club this season.
On the other hand, Vitor Roque hasn't had enough opportunities to play since Xavi prefer Lewandowski over him. However, if Lewandowski leaves the club next season, we may see some changes in their games.