Yes, we've seen Barcelona's trident of Lamine Yamal, Lewandowski, and Rafinha perform quite well and solidly. All three are key players in Barcelona's attack. However, it's important to understand that Lewandowski doesn't always play every game for Barcelona. Age never lies, so to maintain his performance, his playing time on the pitch must be limited. And of course, this leaves little room for Rashford to get on the pitch, even as a substitute. Initially, the coach may not place full trust in Rashford, but if Rashford can prove he deserves to be at Barcelona, it's possible that Rashford will eventually become one of Barcelona's key players.
Because of Lewandowski's age, Rashford might have a chance to play for Barcelona. But yes, it is certain that he will not get a regular chance at the beginning, maybe he will get a chance as a substitute player. If he can use that chance then maybe we will see Rashford as a regular starter in Barcelona's team. Since Barcelona prefers young players, I am not too worried about Rashford's chance, but rather how he will use that chance.