Sanches arrived days after being named best young player at Euro 2016, which Portugal won. Bayern beat several English clubs to the signature and paid a large fee for a teenager with one senior season behind him.
He played very little under Carlo Ancelotti, was loaned to Swansea in 2017-18 where things went worse, and was sold to Lille in 2019 for a fraction of the fee. He later rebuilt his career in France and won a Ligue 1 title.
Why it did not work: this is a fit-and-timing story rather than a talent story. A physical, ball-carrying midfielder needed minutes and a settled coach; Bayern were mid-transition and had neither to offer.
On the fee
The figure above is a reported fee. Bayern, like most German clubs, do not confirm transfer amounts, so contemporary press reporting is the best available record and add-ons are rarely disclosed. Where a fee is disputed, this site says "reported around" rather than quoting a false precision.