Although Sancho returned to Manchester United, but there is no guarantee that Sancho will have the same good performance as Sancho playing in Dortmund. Because after all, previously Sancho also played well in Dortmund and then Manchester United bought Sancho but what happened was, Sancho's performance was not as expected so Manchester United loaned Sancho to Dortmund again.
We can't expect his performance in Man United will be as well as in Dortmund because the tactics may be different and Sancho may not play as the main player in Man United. We know there are 3 left wingers in Man United. They are Rashford, Garnacho, and Sancho. Recently, Garnacho is the most rising player on left winger position. I'm sure Ten Hag will choose Garnacho as the main left winger for the next season. So, I really expect that Sancho will leave permanently from Man United. Joining Dortmund again is surely a good idea.
In such a way, I personally remain convinced that there is no guarantee for Sancho to be able to provide good results at Manchester United. What's more, there are also rumors about Juventus interest in buying Sancho and not only that, because there are also rumors that Juventus are ready to exchange Chiesa to bring Sancho from Manchester United to Juventus. With rumors like this, it seems like any decision could happen, because Juventus will also play in the Champions League next season, and Manchester United only play in the Europa League next season.
I also know the rumor but I think Juventus won't sign Sancho if they still keep Federico Chiesa. As far as I know Juventus has a plan to sign Sancho if they sell Federico Chiesa. Juventus will play in UCL, they must keep the balance of their squad in a good shape. If they lose Federico Chiesa, they must find out another player who has the same level as Federico Chiesa. Sure, Sancho is a good replacement for Federico Chiesa. But I don't know if Sancho is interested to join Juventus. I think Sancho will prioritize to join Dortmund.