So it is clear that Ten Hag's selfish attitude was the main trigger for his failure to bring Manchester United back to its glory days. Therefore, Ten Hag really has to change his attitude if he really wants to be able to bring Manchester United to become champions. And you are right my friend, that this season will definitely be a defining season for Ten Hag. Because if Ten Hag fails this season, he will definitely be fired from Manchester United's coaching.
I removed some part of your post due to how lengthy it is. I don't think Manchester united management is ready to fire Ten Hang because there is no perfect time to fire him than at the end of last season when clubs who were not satisfied with their couch fire them. Everyone expected to wake up to the news of Ten Hang sack but were all shocked hearing that he will continue as the head couch. He has a very good relationship with the management crew and that's what is keeping him. I quite agree that they have players who have potential but then injury is giving them tough time and Ten Hang on the other hand doesn't know how to make good use of the available ones with his preference and selection.
As far as I know Manchester United are banking on their current manager for one more season. Manchester United did not get good results under this manager yet Manchester United gave the manager another chance.
If Manchester United stick to their singular decision this transfer season, if they extend their current manager's contract for another season, I would assume this is the last chance for Ten Hag. If Ten Hag fails to deliver good performance this season, Manchester United will definitely fire this manager without thinking about next season. But now there are rumors that Manchester United could change this manager.
Basically when the transfer window opens there are many such rumors and all kinds of rumors are likely to come true now it remains to be seen whether Manchester United will trust their old manager or hand over the reins of their club to another manager.