The thing about De Ligt “failing” at Juve is a huge myth. He went there very young with Bonnucci and Chielini still there and got loads of game time under three different coaches playing in multiple systems.
By the end of his time there, he was seen as their best player, and Tuchel wanted him at Chelsea. (Tuchel stopped rating him in Bayern stint, but I'd put my house on that being because Tuchel is strange in that way. Case in point, he banished Chalobah after using him for a few months at Chelsea but then wanted to sign him for Bayern.)
Here’s James Horncastle on De Ligt while at Juventus…
“De Ligt was the most promising footballer in his position when Juventus bought him and he was their best defender last season, playing more minutes than any outfield player in the squad. His presence became more pronounced. His performances more authoritative. When Juventus defended well, it was De Ligt who stood out and at only 22, the best is yet to come. He is a foundation stone of the new Juventus.”
Revisionist stuff written last week is likely to be bullshit. De Ligt did fine at Juventus but went at a time when they were badly run. That doesn't mean De Ligt is necessarily the right signing for United, but if he's not, it won't be because “he flopped at Juventus.”