This is far more likely then nobody else wanting him. Making the Brazil squad and maybe being away from the spotlight in Europe might be very healthy for him. He is a talented player that just didn't kick on and was made a bit of a scapegoat for United over the last few years.
Exactly, some people talk as if these players are just commodities to be traded and forget that the player's own preferences and plans come into this.
Four years ago, Pereira decided to go on loan to Valencia after coming back from loan to Granada. Mourinho said he was making the wrong decision and should stay in Manchester and fight for his place and clearly thought then he could make the Utd first team (allow here for Mourinho's bias towards Portuguese and Brazilians). That was after LVG had basically used him as the team interpreter (he speaks Dutch and French as well as English and Portuguese) but rarely played him. He is a talented player, but also overestimates the extent of his talent. He also sees himself as a creative player, maybe in the style of Juan Mata, in a league and a team that doesn't deploy that kind of player in many games (look at how sporadically Mata has been used in his time at Utd). He's not on a high wage, but some people talk as if he is some kind of huge millstone around the club's neck. Granted, for the number of games he plays for us, here is no point him remaining in the team, though. I'm sure he can see that himself - his frustration, which comes out whenever he's interviewed, is he desperately wants to prove himself at Utd.
He was born in Belgium, but clearly identifies as Brazilian. He's 25 now with a wife and young child, so he's at a turning point if there's no prospect of him getting regular playing time at United. It looks to me as if he's reached a point where he's turning to what he sees as his homeland after seasons of loan spells in Spain and Italy and not finding a home.
Regardless of the technical issue of how much the club get for him if he stays at Flamengo (and his contract runs out in June 2023), I'd be surprised if we see him back now. Good luck to the lad, a shame it hasn't worked out at Utd but I wish him no ill and he doesn't deserve the scathing treatment he gets from some posters.