I don't know the reason behind the many reports in the media about a proposed deal that'll see Zinedine Zidane replace current Manchester United manager Erik Ten Hag when the Dutchman leaves the club or whenever he's been sacked but one thing I know for sure is that a manager of Zinedine Zidane's character will not like to manage a Manchester United side that's having some issues concerning the management of the club.
The Glazers tends to have too much direct influence on the Manchester United team and Zidane would want a team which he makes all the vital decisions which Manchester United doesn't fall under that category.
The media posted the rumor because they know it will attract people. We know that Zidane already stated that he is no interested to manage Man United, so we can assume it is a bit impossible for him to replace Ten Hag as a manager of Man United. Moreover, Real Madrid also will have no coach in the next year because Ancelotti will leave Real Madrid. Instead joining Man United, I believe Zidane will be more interested to return to Real Madrid. In addition, Man United owner and management seem not suit with the character of Zidane. Zidane is a typical coach who doesn't want to intervene by the owner and management. He won't feel comfortable to manage a team like Man United that is full of intervened by them.