Great young player but I don't think he is worth 100m, at least in this market.
He dramatically outperformed xg and xa the past two years and then this year his goals and assists came back much more in line with what you would expect from xg and xa (although still getting some assist boost due to playing alongside some great finishers). His topline goals and assists numbers from this year are a better indicator of the underlying abilities to create chances for others and get into scoring positions. In terms of npxg+xa, in his three years in Germany he has finished 30th, 11th, 12th, which is damn impressive for a player who has been in the age 19-21 age bracket but not quite as otherwordly as the topline numbers would suggest. The Bundesliga is also just a high scoring league, especially at the top of the table, with a lot of video game numbers being put up by players from the top sides.
The rest of his game, especially in helping in the build up, is pretty impressive so it is still a very impressive overall package, particularly for a 21-year-old. But I think he is more like a 50-70m player in this market.
For me, United would do better to prioritize first buying a top level CB and then evaluate later in the summer whether you can/should buy Sancho based whether the price moves, whether funds come in through sales, and what else is available on the market. I certainly would not want to commit to buying Sancho for a very big fee early in the summer and then only be able to address CB if enough funds were raised through sales.