I think this should be Barcelona's 2020/21 squad. Due to the coronavirus pandemic they can't spend a lot of money, so I think that Setien decides to involve La Masia more.
Our 1st goalkeeper should definitely be Ter Stegen, provided that he doesn't leave this summer, otherwise we should try to buy Onana. Our central defence seems quite strong with Pique and Lenglet. I think Setien should start to let Lenglet and Umtiti play together, so we can have a dynamic duo in the upcoming years. We also can't forget about Todibo, who is a huge talent and also has the abilities to be a starter in the future.
Our right fullback position is still a weak spot, but I don't know who we could buy (except Kimmich) who would really suit the Barca style. The left defensive flank is quite good with our main man Jordi Alba. I hope Setien introduces Firpo more next season, because he could also become quite good.
Our pivot could either be played by Busquets or De Jong, but I think we should go for the former one, because he gives us more stability and De Jong could learn a lot from playing by his side as an interior. I think Arthur deserves the starting spot as much as De Jong, but I still went for De Jong, because I really could see Coutinho bloom under Setien and he could play the creative role in our midfield three. Our backups would be Alena, Puig and Collado. I really hope none of the gets loaned out or sold, because they are all unique in their own style of play, and they could really add something to our game.
The right wing is occupied by Messi, while Trincao could develop in Messis shadow and learn a lot from him. Griezmann could play as a LW, provided that he adapts to our style of play. Dembele could also take that spot, as long as he's fit. He is still 22 years old and I think he should have one last chance to prove himself. Fati maybe could get a bit to less gametime so I don't know if we should sell one of the two mentioned above.
If we get Lautaro Martinez, he should be our main striker, because he has a extremely high ceiling and he works well together with Messi. Suarez could be our super sub and Braithwaite could also add something to our game with his immense work ethic.

We have some good players out on loan, such as Pedri, Cucu, Rafinha, Oriol Busquets or Miranda, but I don't really see a spot in this squad for them right now. This squad is already overpacked and I doubt, that it will turn out to be our squad next year.

I hope you all stay well and I hope that we can see Barcelona win titels rather sooner than later.