Of course there's no guarantee when there are other players who are much better than him in the same position, and that means it will be very difficult for Rodrygo to secure a starting spot in the team. He's still quite young and there may still be plenty of opportunities for him if he can be patient and continue to improve his individual skills. But if Rodrygo's goal is to play regularly for the national team, perhaps considering other clubs is also a good idea, as long as he can guarantee a spot, as the national team itself has many players in the same position as him.
You are right that he is young and has much of room to improve so being patient could work out for him. But you also made good point that if he wants to play for national team regularly he might need to think about joining another club where he has guaranteed more playing time. This is common problem for talented young players do they stay at big club and fight for chance, or do they move to smaller team to play more and develop faster?