As far as I know, Zidane rejected Man United's offer at that time because he wanted to rest until the summer of 2022 and his wife did not want to stay at Man United. The chances of Man United being able to sign Zidane are very small because it seems that Zidane will still stick to his stance.
Apart from Mauricio Pochettino, other coach candidates being targeted by Man United are Erik Ten Hag, Julen Lopetegui, and Luis Enrique.
https://twitter.com/David_Ornstein/status/1485525496314187777The last I heard is that Pochettino might leave PSG, in which case PSG want Zidane to take his place. But Zidane himself wants to lead the French national team. It's hard to predict how the puzzle will play out, but the likelihood of Zidane ending up at United is very slim. I think United's ability to sign a great manager will depend a lot on where they finish. If it is top 4, then it will be a plus.