Nico and Collado are imo Barca B players with best chances to have first team minutes. For Collado is probably a make or break preseason. If he'll convince Koeman he'll stay if not he'll go on loan or be sold with a buy-back. Don't see him starting another season with Barca B. Nico will play regularly for Barca B and be called up to first team when needed. But with FDJ, Busi and especially Pedri being away on NT duty and having prolonged holidays there will be an open competition for at least one spot on the bench at the start of the season for younger midfielders. Especially as long as Ilaix's future is uncertain.
Also interested how Gavi will do. He's probably the most talented among all but will only turn 17 next month so we shouldn't rush him. He should first establish himself at Barca B before getting a serious look in the first team.
Ramos Mingo could also be someone who Koeman will look at seriously but he has tested positive for Covid so will miss first 10 days of trainings and probably first two preseason games as well. Anyway, if we'll hopefully somehow manage to offload Umtiti we'd still have 5 CBs in first team but only Lenglet is left footed. So if Koeman will want another leftie there could be a chance for Ramos Mingo as well. Don't expect him to get any serious minutes though unless we'll again have injury problems at the position.
And then I'll also focus on Barca B new signings Yusuf Demir, Kays Ruiz and possibly Jordi Escobar who are all training with the first team today alongside Alejandro Balde.