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.
You could be right but sometimes a player perform more when he joined other league, however I don't see anything that will actually hinder the performance of Sancho in Manchester United, I really commend on Manchester United for getting a player like Sancho because watching him performing the way he did on Borussia Dortmund during the champions League move me in liking him, so we are hopeful that his performance will remain the same in Manchester United even if he may no longer be the best player of the club, however in the case of haaland people had the same thought about him but when he started playing everybody became surprised so perhaps that's what may likely happen in the case of Sancho and funny enough he also came from the same club as haaland.
Sancho's future is still unclear. I don't know if will keep him for use in the new season or still resolutely sell him at a reasonable price. There has been a lot of information that Sancho is no longer in Ten Hag's plans and will be put on the transfer market to be sold to another club this summer. MU will try to push this winger away again this summer. Coach Erik ten Hag needs to raise transfer funds to welcome a suitable recruit. Knowing that Sancho's return promises to give MU a quality option on the offensive front, but so far there has been no public apology issued by Sancho after the conflict with coach Ten Hag during the season—Last year. Therefore, I believe that Sancho cannot have good spirit and form like playing for Borussia Dortmund.