Bayern are really dumb letting him go for free, he's a very good defender that could've pocketed them a decent amount needed to replace him.
Bayern desperately need reinforcement at the back. Pavard doesn't play CB well, Nianzou hasn't been getting many opportunities if not injured and Upamenaco has been irratic. Sule and Lucas were the best CB partnership (or Sule, Lucas, Upa as a back 3).
As for United, I'm sort of torn between whether to sign him or not. I don't think he's the elite level defender like VvD or Ruben Dias that we need but he is for free and therefore will be a quality defender for cheap. Him and Maguire can be a really good pairing, if Maguire goes back to his old form.
He's wanted to play in England for ages now, I think many clubs would be eager to get him (Spurs, Chelsea, United being top of the list).
EDIT: I forgot we signed Varane
. Him and Varane would be great, two opposing styles as well with Sule being more aggressive on and off the ball.