Rashford will join the Barcelona squad on loan. Therefore, everything will depend on his performances. I believe Rashford will find success in Spain with his style of play, just like Antony. Antony had a great time at Betis. Rashford will surely do the same.
If he is given the opportunity to play more, I'm sure he will give his best for Barcelona, but the question is whether Hansi Flick will give Rashford a starting spot because, as far as I know, Barcelona's front line is already filled with Lamine Yamal, Rapinha, and Lewandowski. But I think Rashford is only used as a rotation option when Barcelona faces average clubs in the La Liga competition later. Well, when Rashford is given such an opportunity, it should be an opportunity for him to show his best so that management is interested in making him permanent.
I don't think Rashford needs to play against average clubs before he should prove his performance at Barcelona. He can quickly get used to the team if he gets playing time with Hensi flick. Rashford and Raphinha almost play the similar pattern. Raphinha is playing the speed game, and considering their current performance, Marcus Rashford has more speed than Raphinha. I'm not trying to rate Rashford higher than Raphinha because there are several aspects that make Raphinha more valuable than Rashford. Raphinha can play a variety of positions, it would be perfect if Hensi flick used him in the attacking midfield and Rashford on the left wing since that is his natural position.